Data processing apparatus, data processing method, and program

ABSTRACT

A copy control technique using digital watermark information, which makes it possible to prevent a content from being erroneously subjected to a copy control process according to wrong copy control information at a content-to-content transition. Copy control information in the form of digital watermark information (WM) is embedded in a content to control copying of the content in accordance with the embedded copy control information. A content-to-content transition is detected by detecting a change in a content state, such as a change in image luminance, or a change in copy control information associated with a content, or is detected on the basis of a flag, a descriptor, or channel switching. In response to detection of a content-to-content transition, a reset signal is output to a WM analyzer to reset current copy control information into a “undefined” state, so that copy control is performed in a mode such as a copy-free mode assigned to the “undefined” state.

TECHNICAL FIELD

The present invention relates to a data processing apparatus, a dataprocessing method, and a program, for controlling copying of aninformation signal such as an image or audio signal, and moreparticularly, to a data processing apparatus, a data processing method,and a program, for recording, inputting/outputting, or playing back aninformation signal such as an image or audio signal.

BACKGROUND ART

With recent advances in the digital technology, digital record/playbackapparatuses have become popular which are capable of recording andplaying back data many times without causing degradation in image/soundquality. In such a situation, a large number of digital contents ofvarious fields, such as video and music contents, are transmitted anddistributed using recording media such as a DVD or a CD or through acommunication network.

In digital recording/playing back, unlike analog recording/playing back,high quality similar to that of original data can be maintained, becausedata can be recorded and played back repeatedly many times withoutcausing data to be degraded. However, the popularity of suchhigh-quality digital recording/playing back technology results inspreading of a large number of illegally copied data, and thus seriousproblems in protection of copyright have arise.

To protect copyrights of digital contents from being pirated by illegalcopying, it has been proposed to add copy control information forcontrol copying to digital contents and read the copy controlinformation when digital contents are recorded or played back therebypreventing digital contents from illegally copied.

Controlling of copying of contents can be performed in many modesdepending on information sources. For example, any copying is prohibitedin one mode, but in another mode, copying from original data ispermitted only once and further copying from the copied data isprohibited (this mode is called copy generation management).

A typical copy generation management method is known as the CGMS (CopyGeneration Management System) method.

When the CGMS method is applied to an analog video signal, copy controlinformation (CGMS-A information) is described by 2 bits in a total of 20bits of additional information and superimposed on a luminance signal ofa video signal in a specific horizontal interval within a verticalblanking period. In the case of a NTSC video signal, the specifichorizontal interval described above is the 20th effective horizontalinterval. In the case of a digital video signal, 2-bit copy controlinformation (CGMS-D information) is inserted into the digital videodata, and the digital video data is transmitted together with theinserted copy control information.

The 2-bit information according to the CGMS method (hereinafter,referred to as the CGMS information) has one of the following values,depending on the copy control mode: “00” (copying is permitted freely),“10” (copying is permitted once (one-generation copying is permitted)),and “11” (copying is prohibited (unconditionally)).

In a case in which CGMS information added to image information has avalue of “10”, a recording apparatus adapted to the CGMS methoddetermines that the received video signal is permitted to be copied, andrecords the video signal. In this case, CGMS information rewritten into“11” is added to the recorded video signal. On the other hand, in a casein which CGMS information added to video information to be recorded hasa value of “11”, the recording apparatus adapted to the CGMS methoddetermines that the video signal is prohibited to be copied, and therecording apparatus does not record it. An IEEE1394 interface is knownin the art as an interface for digital video data. It has been proposedto use CGMS information to protect copyrights of data transmitted viathe IEEE1394 interface.

In addition to the copy control method using CGMS information, there aremany other known methods for protect copyrights of contents. Forexample, in digital broadcastings performed by broadcasting stations,digital copy control descriptor is stored in serving information (SI)included in a transport stream (TS) packet by which digital data iscarried. When digital data received by a receiver is recorded using arecording apparatus, generation-based copy control is performed inaccordance with the digital copy control descriptor.

It has been proposed to describe copy control information in the form ofa digital watermark (WM) that cannot be viewed or perceived when acontent (such as video data or audio data) in which the digitalwatermark is embedded is played back in a normal manner. When thecontent is processed by an apparatus such as a receiver, a recorder, ora player, the digital watermark (WM) is detected, and generation-basedcopy control is performed in accordance with the detected digitalwatermark (WM).

Because digital watermarks can be detected and embedded only by specificdevices, tampering with data is very difficult. Thus, in this technique,data is highly reliable compared with the CGMS method in which controlinformation is added in the form of bit data.

However, a problem of this technique is that the detected level ofdigital watermark information greatly varies depending on the content ofan information signal (such as a video or audio content) to which adigital watermark is added or various processes such as datacompression, decompression, or scrambling, performed on the signal afterthe digital watermark was added to the content, and thus the time neededto detect the digital watermark information from the content variesdepending on the content.

More specifically, in the process of detecting a digital watermarkembedded in video data, although the digital watermark can be detectedinstantaneously in some cases, there is a possibility that the digitalwatermark cannot be detected in a long continuous period such as fewseconds or few ten seconds depending on the video data.

FIG. 20 shows an example of a process of detecting a digital watermarkembedded as copy control information in data. In this example shown inFIG. 20, a digital watermark is detected when digital data broadcastedfrom a station is received or the received digital data is recorded. Indigital broadcasts provided by broadcasting stations, various programsare provided one after another, and various commercial messages providedby sponsors are inserted between programs. Thus, copyright of contentsprovided via broadcasting varies frequently and sequentially.

In a case in which a digital watermark is embedded as copy controlinformation, a digital watermark functioning as copy control informationindicating that copying should be controlled in the Copy Free mode, theCopy Once mode, or the Never Copy mode is embedded in each content ofprograms and commercial messages.

In the example shown in FIG. 20, a digital watermark functioning as copycontrol information indicating that copying should be controlled in theCopy Once mode is embedded in a content provided during a period A, anda digital watermark functioning as copy control information indicatingthat copying should be controlled in the Copy Free mode is embedded in acontent provided during a period B. In a receiver or a record/playbackapparatus, a digital watermark is detected from a content and thecontent is recorded into a digital device.

When a content having copy control information indicating that copyingshould be controlled in the Copy Once mode is digitally recorded by adigital recording apparatus adapted to recording (playing back) ofcontents according to copy control information, if copy controlinformation indicating that copying should be controlled in the CopyOnce mode is detected from the content, the digital recording apparatusrewrites the copy control information into No More Copy and records thecontent together with the rewritten copy control information. Thus, ifthe content recorded by the digital recording apparatus is tried to befurther recorded into another digital device, copying is prevented bythe copy control information set to No More Copy.

Detection of a digital watermark from a content is performed repeatedlyfor each image frame. However, as described earlier, the levels ofdetected digital watermarks, that is, the detected levels, varydepending on the condition of the video data, and the digital watermarkscannot be accurately detected unless the detected levels are higher thana predetermined threshold (Th). Therefore, the digital watermarks areread only when the detected levels are higher than the threshold (Th).If a digital watermark includes copy control information, copying iscontrolled in accordance with the detected copy control information.More specifically, in accordance with the control information, decidingwhether to permit the operation of recording the content onto arecording medium is performed, and the copy control information isrewritten, for example, from Copy Once to No More Copy.

In FIG. 20, detection timing arrows (denoted by a, b, c, d, e, f, and g)indicate times at which digital watermarks having a level higher thanthe threshold (Th) is successfully detected. If a digital watermark isdetected, the process performed thereafter obeys the detectedinformation at least over a following period with a predetermined length(T). In the case of the content A, because the digital watermarkincluding the copy control information indicating that copying should becontrolled in the Copy Once mode is embedded in the content A, copyingis controlled in accordance with the copy control information indicatingthat copying should be controlled in the Copy Once mode. If no digitalwatermark is detected in a period with the predetermined length (T), thedetected information is determined to be “undefined”, that is, theprocess is performed assuming that that no control information isincluded in the content. There is no obligate rule to be applied to the“undefined” case, and the process for an “undefined” period may beperformed, for example, in a similar manner as is performed when thecontent includes copy control information indicating that copying shouldbe controlled in the Copy Free mode.

In FIG. 20, at a time denoted by a detection timing arrow c, digitalwatermark information is detected from the content A, and the process isperformed in accordance with the detected copy control informationindicating Copy Once. Thereafter, at a time (denoted by an arrow d)within a following period of T, a digital watermark including copycontrol information indicating that copying should be controlled in theCopy Once mode is detected. After that, if the content is switched fromA to B, no digital watermark is detected for a while. In this case, thereceiver or the record/playback apparatus that is processing the contentobeys not to the copy control information (Copy Free) of the content Bbut to the copy control information (Copy Once) of the content A in aninitial period (denoted by “wrong decision” in FIG. 20).

When the digital recording apparatus is recording the content, if thecontent being recorded is switched from the content A including copycontrol information indicating Copy Once to the content B including copycontrol information indicating that copying should be controlled in theCopy Free mode, and if the initial part of the content B (in the “wrongdecision” period in FIG. 20) is processed in accordance with the copyingcontrol information (Copy Once) of the content A as shown in FIG. 20,the initial part of the content B is recorded together with copy controlinformation rewritten to No More Copy indicating that no more copying ispermitted in accordance with the copy control information (Copy Once) ofthe content A, although the initial part of the content A is actuallypermitted to be freely copied. Thus, there occurs a problem that theinitial part of the content B cannot be further copied, although thatpart should be permitted to be copied.

SUMMARY OF THE INVENTION

In view of the above, an object of the present invention is to provide atechnique of controlling copying of a content in accordance with copycontrol information described in the form of a digital watermark thatcannot be easily tampered with, so as to solve the problems caused byvariations in detection timing of digital watermarks at acontent-to-content transition, and so as to prevent a current contentfrom being processed in accordance with wrong copy control informationassigned to a previous content after the previous content is switched tothe current content, thereby ensuring that copying is controlledcorrectly.

According to a first aspect of the present invention, there is provideda data processing apparatus for performing at least one of dataprocesses including a data recording process, a data playing-backprocess, and a data inputting/outputting process, in which copy controlinformation represented in digital watermark information is detected,and copying of data is controlled in accordance with the detected copycontrol information included in the digital watermark information,

the data processing apparatus including digital watermark decoding meansfor detecting a digital watermark embedded in a content and outputtingdetected copy control information as control information applied to acontent to be processed,

the digital watermark decoding means including:

-   -   state change detection means for detecting a transition from a        content to another content having a possibility that copy        control information embedded therein is different from that        embedded in the former content, and outputting a reset signal to        digital watermark information analysis means in response to        detecting of a state change corresponding to the content        transition; and    -   digital watermark information analysis means for resetting        control information applied to the content in accordance with        the reset signal received from the state change detection means,        and outputting, as control information to be applied to the        content, “undefined” control information corresponding to        non-detection of a digital watermark.

In an embodiment of the data processing apparatus according to thepresent invention, if the digital watermark information output from thedigital watermark information analysis means is “undefined”, and if acontent to be processed includes copy control information, addedthereto, other than digital watermark information, the copy controlinformation other than the digital watermark information is employed ascontrol information to be applied to the content.

In an embodiment of the data processing apparatus according to thepresent invention, if the digital watermark information output from thedigital watermark information analysis means is “undefined”, and if acontent to be processed includes copy control information, addedthereto, other than digital watermark information, history of the copycontrol information other than digital watermark information and historyof copy control information described in the digital watermarkinformation are checked to determine whether these two kinds of copycontrol information were consistent with each other over a predeterminedperiod, and, if and only if it is determined that the two kinds of copycontrol information were consistent with each other over that period,the copy control information other than digital watermark information isemployed as copy control information to be applied to the content.

In an embodiment of the data processing apparatus according to thepresent invention, the copy control information other than digitalwatermark information is CGMS (Copy Generation Management System)information.

In an embodiment of the data processing apparatus according to thepresent invention, the state change detection means monitors a change insignal information of a content being processed; and, if a changegreater than a predetermined threshold is detected, the state changedetection means determines that a content-to-content transition hasoccurred, and the state change detection means outputs a reset signal tothe digital watermark information analysis means.

In an embodiment of the data processing apparatus according to thepresent invention, the state change detection means monitors a change incopy control information serving as additional information other thandigital watermark information, added to a content being processed; and,if a change is detected, the state change detection means determinesthat a content-to-content transition has occurred, and the state changedetection means outputs a reset signal to the digital watermarkinformation analysis means.

In an embodiment of the data processing apparatus according to thepresent invention, the state change detection means monitors a change ina descriptor or a flag serving as additional information other thandigital watermark information, added to a content being processed; and,if a change is detected, the state change detection means determinesthat a content-to-content transition has occurred, and the state changedetection means outputs a reset signal to the digital watermarkinformation analysis means.

In an embodiment of the data processing apparatus according to thepresent invention, the state change detection means monitors channelswitching; and, if channel switching is detected, the state changedetection means determines that a content-to-content transition hasoccurred, and the state change detection means outputs a reset signal tothe digital watermark information analysis means.

In an embodiment of the data processing apparatus according to thepresent invention, the state change detection means monitorspresence/absence of an input signal and determines that acontent-to-content transition has occurred when a presence-to-absencetransition, an absence-to-presence transition, or apresence-to-absence-to-presence transition is detected, and the statechange detection means outputs a reset signal to the digital watermarkinformation analysis means in response to the detection of thecontent-to-content transition.

According to a second aspect of the present invention, there is provideda data processing method of performing at least one of data processesincluding a data recording process, a data playing-back process, and adata inputting/outputting process, in which copy control informationrepresented in digital watermark information is detected, and copying ofdata is controlled in accordance with the detected copy controlinformation included in the digital watermark information,

the data processing method including a digital watermark decoding stepof detecting a digital watermark embedded in a content and outputtingdetected copy control information as control information applied to acontent to be processed,

the digital watermark decoding step including the steps of:

-   -   detecting a transition from a content to another content having        a possibility that copy control information embedded therein is        different from that embedded in the former content, and        outputting a reset signal to digital watermark information        analysis means in response to detecting of a state change        corresponding to the content transition; and    -   resetting control information applied to the content in        accordance with the input reset signal, and outputting, as        control information to be applied to the content, “undefined”        control information corresponding to non-detection of a digital        watermark.

In an embodiment of the data processing method according to the presentinvention, if the digital watermark information output from the digitalwatermark information analysis means is “undefined”, and if a content tobe processed includes copy control information, added thereto, otherthan digital watermark information, the copy control information otherthan the digital watermark information is employed as controlinformation to be applied to the content.

In an embodiment of the data processing method according to the presentinvention, if the digital watermark information output from the digitalwatermark information analysis means is “undefined”, and if a content tobe processed includes copy control information, added thereto, otherthan digital watermark information, history of the copy controlinformation other than digital watermark information and history of copycontrol information described in the digital watermark information arechecked to determine whether these two kinds of copy control informationwere consistent with each other over a predetermined period, and, if andonly if it is determined that the two kinds of copy control informationwere consistent with each other over that period, the copy controlinformation other than digital watermark information is employed as copycontrol information to be applied to the content.

In an embodiment of the data processing method according to the presentinvention, the copy control information other than digital watermarkinformation is CGMS (Copy Generation Management System) information.

In an embodiment of the data processing method according to the presentinvention, the state change detection step includes monitoring a changein signal information of a content being processed; and, if a changegreater than a predetermined threshold is detected, determining that acontent-to-content transition has occurred and outputting a reset signalto the digital watermark information analysis means.

In an embodiment of the data processing method according to the presentinvention, the state change detection step includes monitoring a changein copy control information serving as additional information other thandigital watermark information, added to a content being processed; and,if a change is detected, determining that a content-to-contenttransition has occurred and outputting a reset signal to the digitalwatermark information analysis means.

In an embodiment of the data processing method according to the presentinvention, the state change detection step includes monitoring a changein a descriptor or a flag serving as additional information other thandigital watermark information, added to a content being processed; andif, a change is detected, determining that a content-to-contenttransition has occurred and outputting a reset signal to the digitalwatermark information analysis means.

In an embodiment of the data processing method according to the presentinvention, the state change detection step includes monitoring channelswitching; and, if channel switching is detected, determining that acontent-to-content transition has occurred, outputting a reset signal tothe digital watermark information analysis means.

In an embodiment of the data processing method according to the presentinvention, the state change detection step includes monitoringpresence/absence of an input signal, determining that acontent-to-content transition has occurred when a presence-to-absencetransition, an absence-to-presence transition, or apresence-to-absence-to-presence transition is detected, and outputting areset signal to the digital watermark information analysis means inresponse to detection of the content-to-content transition.

According to a third aspect of the present invention, there is provideda computer program for causing a computer system to execute at least oneof data processes including a data recording process, a dataplaying-back process, and a data inputting/outputting process, in whichcopy control information represented in digital watermark information isdetected, and copying of data is controlled in accordance with thedetected copy control information included in the digital watermarkinformation,

the computer program including a digital watermark decoding step ofdetecting a digital watermark embedded in a content and outputtingdetected copy control information as control information applied to acontent to be processed,

the digital watermark decoding step including the steps of:

-   -   detecting a transition from a content to another content having        a possibility that copy control information embedded therein is        different from that embedded in the former content, and        outputting a reset signal to digital watermark information        analysis means in response to detecting of a state change        corresponding to the content transition; and    -   resetting control information applied to the content in        accordance with the input reset signal, and outputting, as        control information to be applied to the content, “undefined”        control information corresponding to non-detection of a digital        watermark.

The computer program according to the present invention may be suppliedto a general-purpose computer system capable of executing variousprogram codes, via a communication medium or a computer-readable storagemedium in which the program is stored.

By providing such a program in a computer-readable form, it becomespossible for a computer system to execute a process in accordance withthe program. By installing a particular computer program onto a computersystem, it becomes possible to achieve a cooperative operation on thecomputer system so as to achieve functions similar to those achieved bythe other aspects of the present invention.

These and other objects and features of the present invention willbecome more apparent from the following detailed description ofembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a system using a generation-basedinformation signal control method according to an embodiment of thepresent invention.

FIG. 2 is a block diagram showing an example of a construction of aset-top box used in the system shown in FIG. 1.

FIG. 3 is a block diagram showing a method of superimposing digitalwatermark information used by the set-top box according to theembodiment shown in FIG. 2.

FIG. 4 is a diagram showing digital watermark information used in theembodiment according to the present invention.

FIG. 5 is a block diagram showing a construction of a WM decoder in theset-top box according to the embodiment shown in FIG. 2.

FIG. 6 is a block diagram showing a construction of a WM analyzer of theWM decoder shown in FIG. 5.

FIG. 7 is a block diagram showing an example of a construction of astate change detector of the WM decoder shown in FIG. 5.

FIG. 8 is a diagram showing a copy control process performed when acontent-to-content transition occurs, according to the presentinvention.

FIG. 9 is a flow chart showing a sequence of updating/resetting digitalwatermark information WM performed by the WM analyzer, according to thepresent invention.

FIG. 10 is a block diagram showing an example of a construction of aninformation signal recording apparatus according to an embodiment of thepresent invention.

FIG. 11 is a block diagram showing an example of a construction of a WMrewriter that is a part of the recording apparatus shown in FIG. 10.

FIG. 12 is a block diagram showing an example of a construction of a WMdecoder that is a part of the recording apparatus shown in FIG. 10.

FIG. 13 is a block diagram showing an example of a WM analyzer that is apart of the WM decoder shown in FIG. 12.

FIG. 14 is a flow chart showing a sequence of updating/resetting digitalwatermark information WM performed by the WM analyzer, according to thepresent invention.

FIG. 15 is a flow chart showing a processing operation performed by therecording apparatus shown in FIG. 10.

FIG. 16 is a block diagram showing an example of a compliant playbackapparatus used in an embodiment according to the present invention.

FIG. 17 is a flow chart showing a processing operation performed by theplayback apparatus shown in FIG. 16.

FIG. 18 is a flow chart showing a processing operation performed by theplayback apparatus shown in FIG. 16.

FIG. 19 is a flow chart showing a digital output control processperformed by the playback apparatus shown in FIG. 16.

FIG. 20 is a diagram showing a copy control process performed when acontent-to-content transition occurs, according to a conventionaltechnique.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a data processing apparatus, a data processing method,and a program, according to the present invention, are described belowwith reference to the accompanying drawings. In the present invention,copy control information described in the form of digital watermarkinformation WM is stored various kinds of data such as videoinformation, audio information, or a program. In embodiments describedbelow, according to the present invention, by way of example,information to be copy-controlled is video information recorded in theform of digital data on a disk recording medium (such as a DVD (DigitalVideo Disk)), and both CGMS information and digital watermarkinformation WM are used as additional information used to performgeneration-based copy control.

Copy control information in the form of digital watermark informationembedded in a content may be set to, for example, one of the followingfour copy control modes:

(1) “Copy Free” mode: content is permitted to be copied freely

(2) “Copy Once” mode: content is permitted to be copied once

(3) “No More Copy” mode: further copying of content is not permitted

(4) “Never Copy” mode: copying is never permitted

One of the four copy control modes is selected depending on a contentsuch as video data or music data and embedded in the content.

In a case in which the copy control information is set to (1) “CopyFree” mode, a content such as music data or video data is permitted tobe copied freely. In a case in which the copy control information is setto (2) “Copy Once” mode, a content such as music data or video data ispermitted to be only once. If a content such as music data or video dataset to (2) “Copy Once” mode is copied, the copy control information isrewritten into the (3) “No More Copy” mode indicating that no morecopying is permitted. In a case in which the copy control information isset to (4) “Never Copy” mode, a content is never permitted.

In a case in which digital watermark information superimposed on videodata or music data has a value corresponding to “Copy Once”, a recordingapparatus adapted to the digital watermark processing (that is, arecording apparatus adapted to the copy control processing) determinesthat the video data or the music data is permitted to be copied, and therecording apparatus records it. In this case, the digital watermarkinformation is rewritten to “No More Copy” and superimposed on therecorded video data or music data. In a case in which digital watermarkinformation superimposed on video data or music data to be recordedindicates “No More Copy”, the recording apparatus adapted to the digitalwatermark processing determines that the video data or the music data isprohibited to be copied, and the recording apparatus does not record it.

In the present embodiment, the digital watermark processing is performedsuch that additional information for performing generation-based copycontrol is modulated by means of a spread spectrum technique using aseries of PN (Pseudorandom Noise) codes, and the resultant informationis superimposed as digital watermark information WM on videoinformation.

When data is recorded on a rewritable recording medium using a recordingapparatus, the data is encrypted by means of scrambling according to apredetermined scheme.

In the following description, a rewritable DVD will be referred to as aRAM disk, and an unrewritable read-only DVD will be referred to as a ROMdisk. A recording apparatus or a playback apparatus adapted to thegeneration-based copy control will be referred to as a compliantapparatus, and an apparatus that is not adapted to the generation-basedcopy control will be referred to as a noncompliant apparatus.Information for controlling copying on the basis of generation will bereferred to as copy control information.

In a case in which an information signal is recorded on a ROM disk in amode in which any copying of the information signal is prohibited,additional information indicating that copying of the information signalis prohibited is added to the information signal recorded on the ROMdisk, and the information signal and the additional information areencrypted according to the CSS (Contents Scramble System) method. Notethat the encryption scheme employed herein for ROM disks is differentfrom that employed in writing data on a RAM disks.

In the present embodiment described below with reference to FIG. 1, adigital broadcast transmitted via a cable or a radio wave is received bya set-top box (receiver) 100 or the like, and the received signal isrecorded on a RAM disk 30 by a recording apparatus 200 disposedseparately from the receiver. The signal recorded on the RAM disk 30 isplayed back by a playback apparatus 300.

In the present embodiment, the set-top box 100 serves as an apparatusfor outputting an information signal. Herein, it is assumed that areceived video signal includes both CGMS information and digitalwatermark information WM, functioning as copy control information.Basically, when the video information is output from the set-top box100, the CGMS information of the output video information is rewrittenin accordance with the digital watermark information WM such that noinconsistency occurs between the CGMS information and the digitalwatermark information. More specifically, the digital watermarkinformation WM that is difficult to tamper with and the CGMS informationthat is relatively easy to tamper with are compared with each other. Ifthere is inconsistency, the copy control information described in thedigital watermark information WM that is difficult to tamper with isdetermined to be reliable, and the CGMS information is rewritten inaccordance with the digital watermark information WM and the resultinformation is output.

However, digital watermark information cannot be always readcontinuously from a content, and the level of detected digital watermarkinformation varies depending on the content of an information signal(such as a video or audio content) including additional digitalwatermark or various processes such as data compression, decompression,or scrambling, performed on the signal after the digital watermark wasadded to the content.

Therefore, in the process of detecting digital watermark information(WM), digital watermarks are read only when the detected levels arehigher than a threshold (Th). If the detected level is higher than thethreshold (Th) and if the detected digital watermark includes copycontrol information in one of modes (1) to (4) described above, copyingis controlled in accordance with the copy control information. In thecase in which the detected level is higher than the threshold (Th) andcopy control information in one of modes (1) to (4) is detected from thedigital watermark, the process is performed in accordance with thedetected digital watermark (WM) over a following holding period with apredetermined length of T. If another digital watermark having a signallevel higher than the threshold (Th) is detected successfully withinthat holding period T, copying is controlled in accordance with the copycontrol information included in this newly detected digital watermarkover a following holding period T.

As described above, if a new digital watermark is detected in a holdingperiod T, a process is performed in accordance with the newly readinformation. However, if the digital watermark signal level does notexceed the threshold (Th) over a whole holding period T, and thus anynew digital watermark is not detected, the copy control information isregarded as being in an undefined state, and the process is performed ina mode assigned to the “undefined” state. The mode assigned to the“undefined” state may be similar to the mode (1) of “Copy Free”described above, if there is any other copy control information thatshould be applied. However, if there is other copy control informationsuch as CGMS information that should be applied, the process may beperformed in accordance with copy control information described in theCGMS information.

In the present embodiment, in which both CGMS information and digitalwatermark information WM are added as copy control information, if thedigital watermark signal level is not high enough and does not exceedthe threshold (Th) over a continuous period equal to or longer than apredetermined time (T), copy control information detected from thedigital watermark information WM is determined to be “undefined”, andthe CGMS signal is directly output as copy control information withoutrewriting the CGMS signal according to the digital watermark informationWM.

Also in the playback apparatus 300, CGMS information associated withvideo information output therefrom is rewritten in accordance with copycontrol information detected from digital watermark information WM sothat no inconsistency occurs between the CGMS information and thedigital watermark information. That is, in a case in which CGMSinformation and digital watermark information are inconsistent with eachother, copy control information obtained from the digital watermarkinformation WM, which is more difficult to tamper, is determined to bemore reliable than the CGMS information, and the CGMS information isrewritten in accordance with the digital watermark information WM andoutput.

However, also in the playback apparatus 300, if the digital watermarksignal level is not high enough and does not exceed the threshold (Th)over a continuous period equal to or longer than a predetermined time(T), copy control information detected from the digital watermarkinformation WM is determined to be “undefined”, and the CGMS signal isdirectly output as copy control information without rewriting the CGMSsignal according to the digital watermark information WM.

In the recording apparatus 200 according to the present embodiment, in acase in which digital watermark information included in a video signalprovided from the receiver indicates that copy should be controlled inthe “Copy Once” mode, when the received signal supplied from thereceiver is recorded by the recording apparatus 200, if the recordingapparatus 200 is compliant, the CGMS information is rewritten by therecording apparatus 200 into “11” (Never Copy) in accordance with thedigital watermark information WM, and the digital watermark informationWM is rewritten from “Copy Once” to “No More Copy”.

In a case in which the digital watermark signal level is not high enoughand does not exceed the threshold (Th) over a continuous period equal toor longer than a predetermined time (T) and thus copy controlinformation detected from the digital watermark information WM isdetermined to be “undefined”, if the CGMS information has a value of“10” (Copy Once), then, when a received signal supplied from thereceiver is recorded by the compliant recording apparatus, the CGMSinformation is rewritten, as in the previous case, by the compliantrecording apparatus from “10” (Copy Once) to “11” (Never Copy), and thedigital watermark information WM is rewritten into “No More Copy”.

In the present embodiment in which the digital watermark is modulated bymeans of the spread spectrum technique, when the digital watermarkinformation WM is rewritten, the digital watermark informationindicating “Copy Once” is not deleted, but the digital watermarkinformation WM indicating “No More Copy” is superimposed, using adifferent series of PN codes different in the spread spectrummodulation, on the digital watermark information WM indicating CopyOnce.

In this case, the copy control information modulated by means of thespread spectrum technique is superimposed on video information that isthe main information signal such that the spread-spectrum copy controlinformation has a much lower level than the level of the videoinformation. Because the copy control information indicating “Copy Once”and that indicating “No More Copy” are respectively modulated usingdifferent series of PN codes, both pieces of copy control informationcan be detected. If copy control information having a mode closer to theNever Copy mode is employed as copy control information of the currentdigital watermark, the resultant effects are equivalent to thoseachieved when the copy control information is actually rewritten. In thefollowing description, it is assumed that when a plural pieces of copycontrol information are detected from digital watermark information WMin a process of checking the digital watermark information WM, one pieceof copy control information selected in the above described manner isemployed as the result of the checking process.

In the present embodiment, transmission of digital video informationbetween the set-top box 100 and the recording apparatus 200 andtransmission between the playback apparatus 300 and the recordingapparatus 200 are performed, if they are compliant, in a MPEG-compressedform via an interface according to the IEEE1394 standard. When theinterface according to the IEEE1394 standard transmits digitalinformation, the digital information is encrypted to prevent the digitalinformation from being fraudulently copied. Furthermore, the IEEE1394interface determines whether a destination apparatus is compliant andwhether it is a recording apparatus. The IEEE1394 interface also checksadditional information (usually, CGMS information) for generation-basedcopy control and determines, depending on the result of the checking,whether to transmit a key used to decrypt the encrypted digitalinformation.

The communication control scheme described above is called an IEEE1394secure bus. Use of a digital interface according to this scheme makes itpossible to effectively prevent video data from being fraudulentlycopied.

In the present embodiment, The additional information forgeneration-based copy control, which is checked to determined whether ornot the key necessary in decryption should be transmitted, is acquiredfrom the digital watermark information WM. Alternatively, the decisionas to whether the key necessary in decryption should be transmitted maybe made in accordance with the CGMS information that has been rewrittenin accordance with the digital watermark information.

Now, examples of constructions of the set-top box (receiver) 100, therecording apparatus 200, and the playback apparatus 300 are describedbelow. In the following description on the present embodiment, it isassumed that a broadcast signal includes superimposed digital watermarkcopy control information, which is modulated by means of the spreadspectrum scheme using a first PN code series PNa, and which is rewrittenby a compliant recording apparatus by further superimposing digitalwatermark copy control information modulated by means of the spreadspectrum scheme using a second PN code series PNb (different from PNa)so as to perform generation-based copy control.

In the following description, for the purpose of simplicity, digitalwatermark information indicating that copying should be controlled inthe “Copy Once” mode is simply represented as “Copy Once”, digitalwatermark information indicating that copying should be controlled inthe “No More Copy” mode is simply represented as “No More Copy”, anddigital watermark information indicating that copying should becontrolled in the “Never Copy ” mode is simply represented as “NeverCopy”.

[Set-Top Box]

FIG. 2 is a block diagram showing an example of a construction of theset-top box 100 according to the present embodiment.

As shown in FIG. 2, in response to a channel selection operationperformed by a user, a channel selection control signal is supplied to achannel selector 101 from a controller 110. The channel selector 101selects a channel in accordance with the received channel selectioncontrol signal and supplies a broadcast signal of the selected channelto a descrambler 102. The descrambler 102 descrambles the broadcastsignal. The resultant descrambled signal of the selected channel issupplied to a demultiplexer 103. The broadcast signal output from thechannel selector 101 includes a plurality of broadcast programs, andbroadcast program data is selected in accordance with a selectioncontrol signal which is generated by a controller 110 in accordance witha program selection operation performed by a user.

Video data Di of the selected broadcast program output from thedemultiplexer 103 has an MPEG-compressed form. Thus, before the videodata Di is supplied to a display monitor or the like, the video data Dioutput from the demultiplexer 103 is supplied to a video data decoder105 via a CGMS rewriter 104 to MPEG-decode it into an originaluncompressed form. The resultant MPEG-decoded data is converted into ananalog signal by a D/A converter 106 and supplied to the display monitoror the like via an analog output terminal 111 a.

In the present embodiment the video data Di in the MPEG-compressed formoutput from the demultiplexer 103 is supplied not only to the CGMSrewriter 104 as described above but also to a digital watermarkinformation decoder (hereinafter referred to as a WM decoder) 107. TheWM decoder 107 extracts digital watermark information WM added to thebroadcast program data and analyzes the copy control information. Theanalysis result is supplied to the controller 110.

In the present embodiment, digital watermark information WM is included,in the form of a superimposed spread-spectrum signal, in a video signal.The superimposing is performed, as described earlier such that a PN codeused as a spread code is generated at a sufficiently high frequency andadditional information functioning as copy control information ismultiplied by the generated PN code so as to modulate the additionalinformation into a spread spectrum signal thereby converting the copycontrol information having a high signal level with a narrow frequencyband into a low-level signal with a wide frequency band that imposes noinfluence on the video signal. The resultant spread-spectrum copycontrol information is then superimposed on the video data andtransmitted.

FIG. 3 is a block diagram showing a process of superimposing digitalwatermark information WM on a video signal serving as an informationsignal. The superimposing process is performed at a broadcastingstation. In some cases, a video signal on which digital watermarkinformation WM has been already superimposed is broadcasted by abroadcasting station.

In FIG. 3, a sync detector 41 detects a vertical sync signal from avideo signal Vi and supplies the detected sync signal to a timing signalgenerator 42. The timing signal generator 42 generates a timing signalsynchronously with the vertical sync signal.

A PNa generator 43 generates, in synchronization with the timing signalsupplied from the timing signal generator 42, a PN code series PNahaving a periodic pattern repeating with a period equal to the period ofthe vertical sync signal and supplies the generated PN code series PNato an SS (Spread Spectrum) spreader.

A copy control information generator 45 generates copy controlinformation to be superimposed as digital watermark information on thevideo signal Vi, in synchronization with the timing signal supplied fromthe timing signal generator 42, and the copy control informationgenerator 45 supplies generated copy control information to the SSspreader 44. In the above process, the copy control information to besuperimposed is generated so as to indicate “Copy Free”, “Copy Once,” or“Never Copy” determined depending on the information to be transmitted.

The SS spreader 44 multiplies the copy control information by the PNcode series PNa thereby generating a spread spectrum signal. The SSspreader 44 supplies the generated spread spectrum signal to a digitalwatermark information WM superimposer 47 via a level controller 46. TheWM superimposer 47 superimposes the received spread spectrum signal asdigital watermark information on the input video signal Vi. The levelcontroller 46 serves to control the level of the superimposed digitalwatermark information so that the superimposed digital watermarkinformation will not cause significant degradation in a played backpicture. More specifically, the spread-spectrum digital watermarkinformation is superimposed such that the level of the superimposedsignal becomes lower than the dynamic range of the video signal.

FIG. 4 shows spectra of a video signal and copy control informationsuperimposed as digital watermark information. The copy controlinformation is a narrow-bandwidth low-bit-rate signal containing a smallamount of information, as shown in FIG. 4( a). If such copy controlinformation is subjected to the spread spectrum modulation, theresultant signal has a wide bandwidth as shown in FIG. 4( b) and has alow level inversely proportional to the bandwidth.

The resultant spread-spectrum signal, that is, the spread-spectrum copycontrol information is superimposed by the WM superimposer 47 on thevideo signal Vi such that, as shown in FIG. 4( c), the level of thespread-spectrum copy control information becomes lower than the dynamicrange of the video signal, thereby substantially preventing the maininformation signal from being degraded. Thus, when the video signal onwhich the spread-spectrum copy control signal is superimposed issupplied to the monitor receiver, a high-quality picture can be playedback substantially without being influenced by the spread-spectrum copycontrol information.

If the spread-spectrum demodulation is performed to detect thespread-spectrum copy control information as described later, thespread-spectrum control information is converted into the originalsignal with the narrow bandwidth as shown in FIG. 4( d). If thebandwidth spread ratio is set to a sufficiently large value, the powerof the demodulated copy control information becomes higher than that ofthe information signal, and thus copy control information can bedetected.

Because the digital watermark information is superimposed on the videosignal over the same period as the video signal and in the samefrequency band as the video signal, it is impossible to remove or modifythe digital watermark information by means of a frequency filter or bymeans of simple information replacement.

This means that the spread-spectrum copy control informationsuperimposed on the video signal cannot be removed and thus it cannot beeasily tampered with. Therefore, this copy control technique surelyprevents the video signal from being fraudulently copied.

In this technique, furthermore, because spread-spectrum modulation isperformed using a PN code series having a period equal to the period ofthe vertical sync signal in synchronization with the vertical syncsignal, a PN code series used to perform the spread-spectrumdemodulation to detect the spread-spectrum signal from the video signalcan be easily generated on the basis of a signal synchronous with thevertical sync signal detected from the video signal.

The WM decoder 107 for extracting the spread-spectrum copy controlinformation superimposed as digital watermark information WM andanalyzing the detected copy control information can be constructed asshown in FIG. 5. That is, as shown in FIG. 5, the video data Di outputfrom the demultiplexer 103 is supplied to a despreader 1074 and a syncdetector 1071. The video data Di output from the demultiplexer 103 isalso supplied to a state change detector 1076. The sync detector 1071detects vertical synchronization timing and supplies the detectedvertical synchronization timing signal to a timing signal generator1072. The state change detector 1076, detects the timing of acontent-to-content transition, for example, on the basis of the videodata Di, and outputs detection information to a WM analyzer 1075.

The timing signal generator 1072 supplies a vertical synchronizationtiming signal to a PNa generator 1073. The PNa generator 1073 generatesa PN code series identical to that generated by the PNa generator 43 inthe apparatus, shown in FIG. 3, in which the superimposing is performed,such that the PN code series PNa is generated with the same verticalsynchronization timing as that in the apparatus in which thesuperimposing is performed. The PN code series PNa output from the PNagenerator 1073 is supplied to the despreader 1074 to obtain copy controlinformation described in the spread-spectrum digital watermarkinformation WM. The obtained copy control information is supplied to theWM analyzer 1075 to detect the copy control mode. A signal indicatingthe detected copy control mode is supplied to the controller 110.

FIG. 6 shows a construction of the WM analyzer 1075. If the detecteddigital watermark information WM is supplied from the despreader 1074 tothe WM analyzer 1075, a WM level evaluator 3011 in the WM analyzer 1075evaluates the signal level of the detected digital watermark informationWM. More specifically, the WM level evaluator 3011 compares with thedetected signal level with a predetermined threshold (Th). If and onlyif the detected signal level is higher than the predetermined threshold(Th), the WM level evaluator 3011 determines that the copy controlinformation acquired from the digital watermark information WM is valid,and the WM level evaluator 3011 requests a WM information updater 3012to perform an updating process on the basis of the copy controlinformation detected from the digital watermark information.

In a case in which the signal level of the detected digital watermarkinformation WM supplied from the despreader 1074 to the WM analyzer 1075is lower than the threshold (Th), the WM information updater 3012 holdsthe previously detected digital watermark information WM and outputs thedigital watermark information WM to the controller 110 (FIG. 3) so thatthe copying control is continuously performed in accordance with thesame digital watermark information WM.

The comparison of the signal level of the detected digital watermarkinformation WM supplied from the despreader 1074 with the threshold (Th)may be performed by the WM level evaluator 3011 immediately when eachdigital watermark information WM is input to the despreader 1074.Alternatively, the detected signal level may be integrated over apredetermined period of time, and the resultant integral value may becompared with the threshold value. In the case in which the integralvalue is employed, the integral value is reset each time the comparisonresult is obtained. Furthermore, the resetting of the integral value mayalso be performed when the WM information updater 3012 resets the WMinformation.

A holding timer 3013 measures the time elapsed from a time at which theupdate request was output from the WM level evaluator 3011. If the WMlevel evaluator 3011 does not acquire next digital watermark informationWM having a signal level higher than the threshold (Th) and does notoutput a new update request during a period of time with a predeterminedlength (T), the holding timer 3013 outputs a reset signal to the WMinformation updater 3012. If the WM information updater 3012 receivesthe reset signal from the holding timer 3013, the WM information updater3012 resets the digital watermark information WM held therein andoutputs “undefined” information indicating that the digital watermarkinformation is in an “undefined” state to the controller 110.

As described earlier, when the digital watermark information is in the“undefined” state, the process may be performed in a similar manner asin the “Copy Free” mode, if there is any other copy control informationthat should be applied. However, if there is other copy controlinformation (CGMS) as is the case in the present embodiment, that othercopy control information may be applied.

In the present embodiment, in which both CGMS information and digitalwatermark information WM is added as copy control information, if thedigital watermark signal level is not high enough and does not exceedthe threshold (Th) over a continuous period equal to or longer than thepredetermined time (T), and, as a result, copy control informationdetected from the digital watermark information WM is determined to be“undefined”, the CGMS information may be directly applied as copycontrol information.

In the case in which the CGMS information is applied, the digitalwatermark information may be updated in accordance with the CGMSinformation. More specifically, in the case in which CGMS information ofa received content has a value of “10” (Copy Once), and the CGMSinformation is rewritten into “11” (Never Copy) when the receivedcontent is recorded, the digital watermark information WM may be changedinto “No More Copy” in response to the rewriting of the CGMSinformation.

However, because there is a possibility that CGMS information has beentampered with, it is desirable to verify the reliability of the CGMSinformation and perform the rewriting of digital watermark informationWM in accordance with CGMS information be performed only when thereliability is determined to be high enough.

The evaluation of the reliability of CGMS information may be performed,for example, as follows. CGMS information and digital watermarkinformation WM of a content received in a past period with apredetermined length of T1 are compared with each other. If these twopieces of copy control information are consistent with each other over aperiod of time with a length equal to or longer than T2 (T2≦T1) in thepast period, then the CGMS information is determined to be high inreliability. However, if the period in which the two pieces of copycontrol information are consistent with each other is shorter than T2,the CGMS information is determined to be low in reliability.

The state change detector 1076 in the WM decoder 107 monitors the videodata Di input to the state change detector 1076 to detect a change incontent. If the state change detector 1076 detects a change in content,the state change detector 1076 outputs a reset signal to the WMinformation updater 3012 (FIG. 6) of the WM analyzer 1075, in accordancewith the change in content.

The detection by the state change detector 1076 as to acontent-to-content transition may be performed in many ways as describedbelow.

(1) Luminance information of video data Di is monitored. If an abruptchange in luminance is detected at a point, that point is determined asa scene change point at which a content-to-content transition occurs.This method is called a scene change-based detection method.

(2) CGMS information of video data Di is monitored, and a point at whicha change in CGMS information is detected is determined to be a point atwhich a content-to-content transition occurs. This method is called aCGMS-based detection method.

(3) A copy control flag (such as a digital copy control descriptor in SI(Service Information) included in a transport stream (TS) packet ofdigital data) or the like included in broadcast video data is monitored.If a change in flag is detected, it is determined that acontent-to-content transition has occurred. This method is called aflag-based detection method.

(4) CA (Conditional Access) information or the like serving as aconditional access identifier included in broadcast video data ismonitored. If a change in CA information is detected, it is determinedthat a content-to-content transition has occurred. This method is calleda CA information-based detection method. CA information, as with thecopy control flag described above, is included as a descriptor inservice information (SI) included in a transport stream (TS) packet ofdigital data.

(5) Channel switching performed by a receiver is monitored. When achannel switching is detected, it is determined that acontent-to-content transition has occurred. This method is called achannel switching-based detection method.

(6) Presence/absence of an input signal is monitored. When the inputsignal is changed from a “present” state to an “absent” state, from an“absent” state to a “present” state, or from a “present” state to an“absent” state and further to a “present” state, it is determined that acontent-to-content transition has occurred. This method is called aninput signal-based detection method.

The state change detector 1076 (FIG. 5) is constructed so as to be ableto detect a state change by means of one of a combination of some ofmethods described above. If a state change corresponding to acontent-to-content transition is detected, the state change detector1076 outputs a reset signal (FIGS. 5 and 6) to the WM analyzer 1075.

As shown in FIG. 6, the reset signal output from the state changedetector 1076 is input to the WM information updater 3012 of the WManalyzer 1075. If the WM information updater 3012 receives the resetsignal from the state change detector 1076, the WM information updater3012 resets copy control information held therein. When copy controlinformation is output thereafter, “undefined” is output.

That is, during a period from a content-to-content transition to a timeat which new copy control information is detected from digital watermarkinformation, copy control is performed in the “undefined” mode.

As described earlier, when the digital watermark information WM is inthe “undefined” state, the process may be performed in a similar manneras in the “Copy Free” mode, if there is any other copy controlinformation that should be applied. However, in a case in which there isother copy control information (CGMS information) as is the case in thepresent embodiment, that copy control information (CGMS information) maybe applied, if and only if that other copy control information (CGMSinformation) is determined to be reliable.

As described earlier, the state change detector 1076 may detect a statechange in many ways. For example, in the case in which the detection isperformed according to the method (1) based on a change in luminance ofvideo data, the state change detector 1076 may be constructed as shownin FIG. 7. In this case, a luminance component of input video data ispassed through a lowpass filter 2011 and a differentiator 2012 therebydetecting a quantitative change in the luminance signal that may occurat a scene transition. The detected quantitative change is compared witha predetermined threshold (Th(luminance)). If the luminance change isgreater than the threshold (Th(luminance)), it is determined that acontent-to-content transition has occurred, and a reset signal is outputto the WM analyzer 1075.

In the case in which the CGMS-based detection method (2) is employed, aCGMS signal detector is disposed in the state change detector 1076 orelsewhere in an apparatus. If a change in CGMS information is detected,a reset signal is output to the WM analyzer 1075.

In the case in which the detection is performed according to the method(3) based on a change in the copy control flag such as a digital controldescriptor, or according to the method (4) based on a change in CA(Conditional Access) information, a copy control flag or CA (ConditionalAccess) information is acquired via transport stream (TS) processingmeans, and information indicating a change in the copy control flag orthe CA information is input to the state change detector 1076. The statechange detector 1076 generates a reset signal in accordance with theinput information and supplies it to the WM analyzer 1075.

In the case in which the channel switching-based detection method (5) isemployed, a channel switching signal is input to the state changedetector 1076, and the state change detector 1076 generates a resetsignal in accordance with the input information and supplies it to theWM analyzer 1075. In this case, it is not necessary to input video dataDi to the state change detector 1076 as in the construction shown inFIG. 5, but the channel switching signal output from a user interface ora similar device is input to the state change detector 1076.

In the case in which the input signal-based detection method (6) isemployed, a change in the input signal is detected by means of aconstruction similar to that employed in the detection technique (1) onthe basis of a change in luminance of video data, and the state changedetector 1076 generates a reset signal in response to the detection of achange and supplies it to the WM analyzer 1075.

The state change detector 1076 monitors a change in one of the statesdescribed above or changes of a plurality of states to detect acontent-to-content transition. If a content-to-content transition isdetected, the state change detector 1076 outputs a reset signal to theWM analyzer 1075.

FIG. 8 shows a copy control process performed when a reset signal isoutput from the state change detector 1076. In this example shown inFIG. 8, a digital watermark is detected when digital data broadcastedfrom a station is received or the received digital data is recorded. Indigital broadcasts provided by broadcasting stations, various programsare provided one after another, and various commercial messages providedby sponsors are inserted between programs. Thus, copyright of contentsprovided via broadcasting varies frequently and sequentially.

In FIG. 8, a digital watermark functioning as copy control informationindicating that copying should be controlled in the Copy Once mode isembedded in a content provided during a period A, and a digitalwatermark functioning as copy control information indicating thatcopying should be controlled in the Copy Free mode is embedded in acontent provided during a period B. In a receiver or a record/playbackapparatus, a digital watermark is detected from a content and thecontent is recorded into a digital device.

Detection of a digital watermark from a content is performed repeatedlyfor each image frame. However, as described earlier, the levels ofdetected digital watermarks, that is, the detected levels, varydepending on the condition of the video data, and the digital watermarkscannot be accurately detected unless the detected levels are higher thana predetermined threshold (Th). Therefore, the digital watermarks areread only when the detected levels are higher than the threshold (Th).If a digital watermark includes copy control information, copying iscontrolled in accordance with the detected copy control information.More specifically, deciding whether to permit the operation of recordingthe content onto a recording medium is performed, and the copy controlinformation is rewritten, for example, from Copy Once to No More Copy.

In FIG. 8, detection timing arrows (denoted by a, b, c, d, e, f, and g)indicate times at which digital watermarks having a level higher thanthe threshold (Th) is successfully detected. If a digital watermark isdetected, the process performed thereafter obeys the detectedinformation at least over a following period with a predetermined length(T). In the case of the content A, because the digital watermarkincluding the copy control information indicating that copying should becontrolled in the Copy Once mode is embedded in the content A, copyingis controlled in accordance with the copy control information indicatingthat copying should be controlled in the Copy Once mode. If no digitalwatermark is detected in a period with the predetermined length (T), thedetected information is determined to be “undefined”, that is, theprocess is performed assuming that that no control information isincluded in the content. In this case, the process may be performed in asimilar manner as in the Copy Free mode, as described earlier.Alternatively, CGMS information may be applied if the CGMS informationis sufficiently reliable.

In FIG. 8, at a time denoted by a detection timing arrow c, digitalwatermark information is detected from the content A, and the process isperformed in accordance with the detected copy control informationindicating Copy Once. Thereafter, at a time (denoted by an arrow d)within a following period of T, a digital watermark including copycontrol information indicating that copying should be controlled in theCopy Once mode is detected. After that, if the content is switched fromA to B, this content-to-content transition is detected by the statechange detector 1076, and a reset signal is output from the state changedetector 1076 to the WM analyzer 1075.

In response to the reset signal received from the state change detector1076, the WM analyzer 1075 resets the current copy control informationheld therein to the “undefined” state and outputs the copy controlinformation in the “undefined” state. Thus, as shown in FIG. 8, in aperiod immediately after that the content A is switched to the contentB, copy control is performed in the “undefined” mode until digitalwatermark information WM having a signal level higher than the thresholdis detected next. More specifically, during this period, the copycontrol may be performed in a similar manner as in the Copy Free mode,or performed in accordance with CGMS information if the CGMS informationis reliable.

Thereafter, if digital watermark information associated with the contentB is detected at a detection timing (an arrow e), that is, if digitalwatermark information having a signal level higher than the threshold(Th) is input from the despreader 1074 (FIG. 5) to the WM analyzer 1075,an update request in accordance with copy control information includedin newly detected digital watermark information WM is output to the WMinformation updater 3012 from the WM level evaluator 3011 of the WManalyzer 1075 shown in FIG. 6. In accordance with the update request,the WM information updater 3012 performs an updating process. In thisspecific case, because copy control information of Copy Free is added asdigital watermark information to the content B, the Copy Free mode isapplied in the process performed thereafter.

In the present embodiment, as described above, the state change detector1076 monitors a content-to-content transition and outputs a reset signalto the WM analyzer when a content-to-content transition is detected,thereby resetting the current control mode. This prevents the copycontrol information included in a previous content from beingincorrectly applied to a following content when a content-to-contenttransition occurs.

FIG. 9 shows processing flows in a process of updating/resetting digitalwatermark information WM, performed by the WM analyzer 1075 according tothe present invention.

The WM level evaluator 3011 (FIG. 6) of the WM analyzer compares thesignal level of detected digital watermark information input from thedespreader 1074 (FIG. 5) with the predetermined threshold (Th) (stepS701). In this step, the signal level compared with the threshold (Th)may be an integral of detected digital watermark information, asdescribed earlier. If the signal level of the detected digital watermarkinformation is higher than the threshold (Th), the WM level evaluator3011 outputs, to the WM information updater 3012, an update request inaccordance with copy control information included in the detecteddigital watermark information WM. In accordance with the update request,the WM information updater 3012 updates the copy control informationrepresented in digital watermark information WM (step S702).

On the other hand, if, in the comparison step (step S701) in which thesignal level of the detected digital watermark information is comparedwith the predetermined threshold (Th), the signal level is determined tobe lower than the threshold (Th), the holding timer measures the timeelapsed since latest digital watermark information WM was detected, anddetermines whether the elapsed time has reached a holding time T (stepS705).

After updating the copy control information in the digital watermarkinformation WM in step S702, if the elapsed time has not reached theholding time T, the process proceeds to step S703 to determine whether areset signal has been input. The reset signal detected in step S703 isthat which is generated by the state change detector 1076 for detectinga content-to-content transition and is input to the WM analyzer 1075.

If it is determined in step S703 that the reset signal is input to theWM analyzer 1075 from the state change detector 1076, the copy controlinformation represented in the digital watermark information WM that isheld in the WM analyzer 1075 and has been applied as control informationis reset to the “undefined” state. In a case in which it is determinedin step S705 that the time elapsed since the latest digital watermarkinformation WM was detected has reached the holding time T, the copycontrol information is also reset to the “undefined” state in step S704.

In a case in which digital watermark information WM has beensuccessfully detected, the controller 110 rewrites, using the CGMSrewriter 104, the CGMS information in accordance with the copy controlmode described in the digital watermark information WM detected by theWM analyzer 1075 described above, so that the CGMS information becomesconsistent with the digital watermark information WM. More specifically,if the signal level of detected digital watermark information is higherthan the threshold Th and the elapsed time is within the holding time T,the CGMS information is rewritten in accordance with the digitalwatermark information WM.

For example, when CGMS information associated with received videoinformation has a value of “00” indicating that copying is freelypermitted, if associated digital watermark information WM indicates thatcopying is permitted once (Copy Once), the CGMS information is rewritteninto “10” to indicate that copying is permitted once.

In a case in which when CGMS information associated with received videoinformation has a value of “00” or “10” indicating that copying ispermitted freely or once, if associated digital watermark information WMindicates that no more copying is permitted (No More Copy) or copying isnever permitted (Never Copy), the CGMS information is rewritten into“11”.

However, in a case in which digital watermark information having asignal level higher than the threshold Th is not detected within aperiod of holding time T and digital watermark information is determinedto be “undefined”, or in a case in which the a content-to-contenttransition is detected by the state change detector 1076 and a resetsignal is input to the WM analyzer 1075 whereby the digital watermarkinformation is determined to be “undefined”, rewriting of the CGMSinformation according to the digital watermark information WM is notperformed.

In the present embodiment, because digital watermark information WM ishighly reliable without being easily tampered with, CGMS information isrewritten, without checking the state of the CGMS information, inaccordance with digital watermark information WM so that the CGMSinformation and the digital watermark information become consistent witheach other, thereby making it possible to prevent the CGMS informationand the digital watermark information from becoming inconsistent witheach other and thus making it possible to correctly performgeneration-based copy control.

Furthermore, a content-to-content transition occurs, a current contentswitched to from a previous content can be prevented from beingerroneously subjected to copy control according to copy controlinformation assigned to the previous content.

The compressed digital video data from the CGMS rewriter 104 isdigitally output via an IEEE1394 interface bus. In this outputtingprocess, as described earlier, the IEEE1394 secure bus prevents the datafrom being fraudulently copied.

More specifically, the data output from the CGMS rewriter 104 issupplied to an encryptor 108, and the encryptor 108 encrypts thereceived video data in the compressed form, under the control of thecontroller 110, by using an encryption key that is changed fromcommunication to communication. This encryption process performed by theencryptor 108 is based on an encryption method different from the methodemployed to encrypt an information signal recorded on a RAM disk or aROM disk.

The encrypted data output from the encryptor 108 is supplied to adestination electronic device via an IEEE1394 interface 109 and furthervia an output terminal 111 b. In this process, the IEEE1394 interface109 output the data after converting it into a form which satisfies theIEEE1394 interface specifications.

Furthermore, in this process, the controller 110 communicates with thedestination device via the IEEE1394 interface 109 to determine whetherthe destination device is a compliant device. If the destination deviceis a compliant device, the controller 110 further determines whether thedestination device is a recording apparatus.

Thereafter, the controller 110 determines whether decryption keyinformation necessary to decrypt the encryption performed by theencryptor 108 should be transmitted to the destination device, on thebasis of, in this specific embodiment, the copy control informationdecoded by the WM decoder 107 and the type of the destination deviceindicated by information given through the IEEE1394 interface 109. In acase in which plural pieces of copy control information are output fromthe WM decoder 107, the controller 110 employs copy control informationhaving a control mode closest to the Never Copy mode.

In a case in which the destination device is a non-compliant apparatus,the decryption key information is not transmitted to the destinationdevice. Even when the destination device is a compliant apparatus, ifthe destination device is a recording apparatus and if the “No MoreCopy” or “Never Copy” mode is designated by the digital watermarkinformation WM, the decryption key information is not transmitted to thedestination device.

As described above, the IEEE1394 interface may determine whether totransmit the decryption key to the destination device, on the basis ofCGMS information rewritten by the CGMS rewriter 104. In this case, whenthe destination device is a compliant recording apparatus, if the CGMSinformation has a value of “11”, the decryption key information is nottransmitted to the destination device.

As for the analog video signal output from the D/A converter 105, CGMS-Ainformation may be added thereto in accordance with digital watermarkinformation WM. More specifically, the CGMS-A information is describedby 2 bits of a total of 20 bits of additional information superimposedon a luminance signal of a video signal in a specific horizontalinterval within a vertical blanking period. In the case of a NTSC videosignal, the specific horizontal interval described above is the 20theffective horizontal interval.

As described above, because a video signal is output from the set-topbox 100 after CGMS information is rewritten in accordance with digitalwatermark information WM that is highly reliable without being easilytampered with so that the CGMS information and the digital watermarkinformation become consistent with each other, generation-based copycontrol can be correctly performed even by an apparatus that uses onlyCGMS information.

A decoder for decoding CGMS information added to received video data maybe provided, and, if comparison between the digital watermarkinformation WM decoded by the WM decoder 107 and the CGMS informationdecoded by the CGMS decoder indicates that the copy control modedesignated by the CGMS information is closer to the Never Copy mode, theCGMS information may not be rewritten. Of course, if there is noinconsistency between the CGMS information and the digital watermarkinformation WM, the CGMS information may not be rewritten.

[Compliant Recording Apparatus]

The compliant recording apparatus 200 is described below. FIG. 10 is ablock diagram showing an example of a construction of the compliantrecording apparatus 200.

As shown in FIG. 10, the compliant recording apparatus 200 includes adigital input terminal 200 d for an IEEE1394 interface, and an analoginput terminal 200 a. The digital input terminal 200 d is connected toan IEEE1394 interface 201. The IEEE1394 interface 201 serves tore-convert data, which has been converted to satisfy the IEEE1394 businterface standard, into the original form.

The data output from the IEEE1394 interface 201 is supplied to adecryptor 202. As described earlier, in a case in which an apparatusconnected to the digital input terminal 200 d determines that aninformation signal is permitted to be copied, decryption key informationneeded to decrypt the encrypted information signal is transmitted fromthe apparatus. If the decryptor 202 acquires the decryption keyinformation, it becomes possible to decrypt the encrypted data receivedfrom the IEEE1394 interface 201 into original compressed video data. Thedecrypted video data in the compressed form is supplied to a selector203.

The analog video information input via the analog input terminal 200 ais supplied to a compression encoder 205 via an analog interface 204.After the analog video information is MPEG-compressed by the compressionencoder 205, the resultant video information is supplied to the selector203.

The selector 203 selects either the data output from the decryptor 202or the data output from the encoder 205 in accordance with a selectorcontrol signal generated in response to an input selection operationperformed by a user. The selected data is output from the selector 203.

The data output from the selector 203 is supplied to a recordingcontroller 206 and also to a WM decoder 207. The WM decoder 207 extractsdigital watermark information WM and analyzes it. The analysis result asto the digital watermark information WM is supplied to the controller210.

On the basis of the received analysis result of the digital watermarkinformation WM, the controller 210 determines whether the inputinformation is permitted to be recorded (copied). If recording (copying)is permitted, the controller 210 further determines whether it is neededto rewrite CGMS information or digital watermark information serving ascopy control information.

That is, in the case in which the controller 210 determines, on thebasis of the digital watermark information WM, that recording isprohibited, the controller 210 controls the recording controller 206 andthe recording unit 212 such that recording is not performed.

When the digital watermark information WM indicates that copying isfreely permitted (in the Copy Free mode) or when the digital watermarkinformation WM is “undefined”, the controller 210 controls the recordingcontroller 206 and the recording unit 212 such that recording becomespossible. In this case, although the compressed digital video dataoutput from the recording controller 206 is passed through the WMrewriter 208 and the CGMS rewriter 209, the digital watermarkinformation WM and the CGMS information are not rewritten. Thecompressed digital video data output from the CGMS rewriter 209 issupplied to a scrambler 211.

The scrambler 211 scrambles the received video data according to amethod different from the CSS or the encryption performed by theIEEE1394 interface. The scrambled video data is recorded by therecording unit 212 onto a RAM disk 30.

In the case in which the digital watermark information WM indicates thatcopying is permitted in the Copy Once mode, the controller 210 controlsthe recording controller 206 and the recording unit 212 to record thevideo data. In this case, the digital watermark information WM isrewritten by the WM rewriter 208 into No More Copy (actually,information indicating that no more copying is permitted is superimposedon existing information), and the CGMS information is rewritten by theCGMS rewriter 209 into “11” so as to indicate that no more copying ispermitted.

After the digital watermark information WM and the CGMS information wererewritten, the resultant compressed digital video data is scrambled bythe scrambler 211 and recorded by the recording unit 212 onto the RAMdisk 30.

Because CGMS information is described by 2-bit data placed at a specificlocation in a data stream of video data, the above rewriting process bythe CGMS rewriter 209 may be performed such that the 2-bit data at thespecific location in the data stream is extracted and rewritten into“11”.

On the other hand, because digital watermark information WM is modulatedby means of spread spectrum technique as described earlier, the digitalwatermark information WM rewriter 208 superimposes a new spread-spectrumsignal on the existing signal. FIG. 11 shows an example of aconstruction of the digital watermark information WM rewriter 208. Thisconstruction is similar to that shown in FIG. 3 except for a digitalwatermark information superimposer and some other differences.

That is, in FIG. 11, a sync detector 2081, a timing signal generator2082, an SS spreader 2084, a level controller 2086, and a WMsuperimposer 2088 are respectively similar to the sync detector 41, thetiming signal generator 42, the SS spreader 44, the level controller 46,and the WM superimposer 47.

A first difference of the digital watermark information superimposerfrom that shown in FIG. 3 is in that a switching circuit 2087 isdisposed between the WM superimposer 2088 and the level controller 2086,wherein only when the controller 210 determines to perform recording andrewriting, the switching circuit 2087 is turned on in response to aswitching control signal output from the controller 210.

A second difference from the digital watermark information superimposershown in FIG. 3 is in that a different PN code series is used in thespread spectrum modulation process. More specifically, the PNa generator43 in FIG. 3 is replaced with a PNb generator 2083 which generates acode series PNb different from the code series PNa.

A third difference from the digital watermark information superimposershown in FIG. 3 is in that a copy control information generator 2085,unlike the copy control information generator 45 shown in FIG. 3,generates only copy control information designating the “No More Copy”mode.

The WM decoder 207 for decoding digital watermark information WM may beconstructed as follows. FIG. 12 is a block diagram showing an example ofthe construction of the WM decoder 207. As shown in FIG. 12, the WMdecoder 207 includes a sync detector 2071, a timing signal generator2072, a PNa generator 2073, a PNb generator 2074, a despreader 2075, aWM analyzer 2076, and a state change detector 2077. The state changedetector 2077 detects a content-to-content transition timing and outputstiming information to the WM analyzer 2076. As can be clearly seen fromcomparison with the construction shown in FIG. 5, the WM decoder 207 isdifferent from that shown in FIG. 5 in that it includes the PNbgenerator 2074 in addition to the PNa generator 2073.

The PNb generator 2074 is provided in the WM decoder 207 to deal with acase in which video data recorded on a RAM disk 30 by the recordingapparatus 200 is played back by a compliant playback apparatus and isagain input to the compliant recording apparatus 200.

In the WM decoder 207, the despreader 2075 detects on or two pieces ofcopy control information by means of despreading using the two codeseries PNa and PNb and supplies the detected one or two pieces of copycontrol information to the WM analyzer 2076. The WM analyzer 2076employs copy control information closer to the Never Copy mode.

The construction of the WM analyzer 2076 is shown in FIG. 13. Whendigital watermark information WM is input to the WM analyzer 2076 fromthe despreader 2075, a WM level evaluator 4011 in the WM analyzer 2075evaluates the signal level of the digital watermark information WM andselects copy control information indicating a copy control mode closerto the never copy mode from the two pieces of copy control informationgenerated by means of despreading using the two PN code series PNa andPNb. The selected copy control information is output from the WM levelevaluator 4011. More specifically, the WM level evaluator 4011 compareswith the detected signal level with a predetermined threshold (Th). Ifand only if the detected signal level is higher than the predeterminedthreshold (Th), the WM level evaluator 4011 determines that the copycontrol information acquired from the digital watermark information WMis valid, and the WM level evaluator 4011 selects copy controlinformation indicating a copy control mode closer to the never copy modefrom the two valid pieces of copy control information generated by meansof despreading using the two PN code series PNa and PNb. The WM levelevaluator 4011 then outputs an update request to the WM informationupdater 4012.

In the case in which the signal level of the detected digital watermarkinformation WM input to the WM analyzer 2076 from the despreader 2075 islower than the threshold (Th), the WM information updater 4012 holds theprevious digital watermark information WM and outputs the digitalwatermark information WM to the controller 210 (FIG. 10) so that thecopying control is continuously performed in accordance with the samedigital watermark information WM.

The comparison of the signal level of the detected digital watermarkinformation WM supplied from the despreader 2075 with the threshold (Th)may be performed by the WM level evaluator 4011 immediately when eachdigital watermark information WM is input to the despreader 2075.Alternatively, the detected signal level may be integrated over apredetermined period of time, and the resultant integral value may becompared with the threshold value. In the case in which the integralvalue is employed, the integral value is reset each time the comparisonresult is obtained. Furthermore, the resetting of the integral value mayalso be performed when the WM information updater 4012 resets the WMinformation.

A holding timer 4013 measures the time elapsed from a time at which theupdate request was output from the WM level evaluator 4011. If the WMlevel evaluator 4011 does not acquire next digital watermark informationWM having a signal level higher than the threshold (Th) and does notoutput a new update request during a period of time with a predeterminedlength (T), the holding timer 4013 outputs a reset signal to the WMinformation updater 4012. If the WM information updater 4012 receivesthe reset signal from the holding timer 4013, the WM information updater4012 resets the digital watermark information WM held therein andoutputs “undefined” information indicating that the digital watermarkinformation is in an “undefined” state to the controller 210.

As described earlier, when the digital watermark information is in the“undefined” state, the process may be performed in a similar manner asin the “Copy Free” mode, if there is any other copy control informationthat should be applied. However, if there is other copy controlinformation (CGMS) as is the case in the present embodiment, that othercopy control information may be applied.

In a case in which both CGMS information and digital watermarkinformation WM is added as copy control information, if the digitalwatermark signal level is not high enough and does not exceed thethreshold (Th) over a continuous period equal to or longer than thepredetermined time (T), and, as a result, copy control informationdetected from the digital watermark information WM is determined to be“undefined”, the CGMS information may be directly applied as copycontrol information.

In the case in which the CGMS information is applied, the digitalwatermark information may be rewritten by the WM rewriter 208 inaccordance with the CGMS information. More specifically, in the case inwhich CGMS information of a received content has a value of “10” (CopyOnce), and the CGMS information is rewritten into “11” (Never Copy) whenthe received content is recorded, the digital watermark information WMmay be rewritten into “No More Copy” in response to the rewriting of theCGMS information.

However, because there is a possibility that CGMS information has beentampered with, it is desirable to verify the reliability of the CGMSinformation and perform the rewriting of digital watermark informationWM in accordance with CGMS information be performed only when thereliability is determined to be high enough.

More specifically, for example, storage means for storing historyinformation of the CGMS information and the digital watermarkinformation Wm and comparison means for time-sequentially comparing theCGMS information and the digital watermark information WM to check theconsistency between them are disposed in the WM decoder 207 or the WMrewriter 208 or elsewhere, whereby the reliability of the CGMSinformation is evaluated. For example, CGMS information and digitalwatermark information WM of a content received in a past period with apredetermined length of T1 are compared with each other. If these twopieces of copy control information are consistent with each other over aperiod of time with a length equal to or longer than T2 (T2≦T1) in thepast period, then the CGMS information is determined to be high inreliability. However, if the period in which the two pieces of copycontrol information are consistent with each other is shorter than T2,the CGMS information is determined to be low in reliability.

The state change detector 2077 in the WM decoder 207 monitors the videodata input to the state change detector 2077 to detect a change incontent. If the state change detector 2077 detects a change in content,the state change detector 2077 outputs a reset signal to the WMinformation updater 4012 (FIG. 13) of the WM analyzer 2076, inaccordance with the change in content.

The detection by the state change detector 2077 as to acontent-to-content transition may be performed in many ways as describedbelow.

(1) Luminance information of video data Di is monitored. If an abruptchange in luminance is detected at a point, that point is determined asa scene change point at which a content-to-content transition occurs.This method is called a scene change-based detection method.

(2) CGMS information of video data Di is monitored, and a point at whicha change in CGMS information is detected is determined to be a point atwhich a content-to-content transition occurs. This method is called aCGMS-based detection method.

(3) A copy control flag (such as a digital copy control descriptor in SI(Service Information) included in a transport stream (TS) packet ofdigital data) or the like included in broadcast video data is monitored.If a change in flag is detected, it is determined that acontent-to-content transition has occurred. This method is called aflag-based detection method.

(4) CA (Conditional Access) information or the like serving as aconditional access identifier included in broadcast video data ismonitored. If a change in CA information is detected, it is determinedthat a content-to-content transition has occurred. This method is calleda CA information-based detection method. CA information, as with thecopy control flag described above, is included as a descriptor inservice information (SI) included in a transport stream (TS) packet ofdigital data.

(5) Channel switching performed by a receiver is monitored. When achannel switching is detected, it is determined that acontent-to-content transition has occurred. This method is called achannel switching-based detection method.

(6) Presence/absence of an input signal is monitored. When the inputsignal is changed from a “present” state to an “absent” state, from an“absent” state to a “present” state, or from a “present” state to an“absent” state and further to a “present” state, it is determined that acontent-to-content transition has occurred.

The state change detector 2077 (FIG. 12) is constructed so as to be ableto detect a state change by means of one of a combination of some ofmethods described above. If a state change corresponding to acontent-to-content transition is detected, the state change detector2077 outputs a reset signal (FIGS. 12 and 13) to the WM analyzer 2076.

As shown in FIG. 13, the reset signal output from the state changedetector 2077 is input to the WM information updater 4012 of the WManalyzer 2076. If the WM information updater 4012 receives the resetsignal from the state change detector 2077, the WM information updater4012 resets copy control information held therein. When copy controlinformation is output thereafter, “undefined” is output.

That is, during a period from a content-to-content transition to a timeat which new copy control information is detected from digital watermarkinformation, copy control is performed in the “undefined” mode.

As described earlier, when the digital watermark information is in the“undefined” state, the process may be performed in a similar manner asin the “Copy Free” mode, if there is any other copy control informationthat should be applied. However, in a case in which there is other copycontrol information (CGMS information) as is the case in the presentembodiment, that copy control information (CGMS information) may beapplied, if and only if that other copy control information (CGMSinformation) is determined to be reliable.

As described earlier, the state change detector 2077 may detect a statechange in many ways. For example, in the case in which the detection isperformed according to the method (1) based on a change in luminance ofvideo data, the state change detector 2077 may be constructed as shownin FIG. 7. In this case, a luminance component of input video data ispassed through a lowpass filter 2011 and a differentiator 2012 therebydetecting a quantitative change in the luminance signal that may occurat a scene transition. The detected quantitative change is compared witha predetermined threshold (Th(luminance)). If the luminance change isgreater than the threshold (Th(luminance)), it is determined that acontent-to-content transition has occurred, and a reset signal is outputto the WM analyzer 2076.

In the case in which the CGMS-based detection method (2) is employed, aCGMS signal detector is disposed in the state change detector 2077 orelsewhere in an apparatus. If a change in CGMS information is detected,a reset signal is output to the WM analyzer 2076.

In the case in which the detection is performed according to the method(3) based on a change in the copy control flag such as a digital controldescriptor, or according to the method (4) based on a change in CA(Conditional Access) information, a copy control flag or CA (ConditionalAccess) information is acquired via transport stream (TS) processingmeans, and information indicating a change in the copy control flag orthe CA information is input to the state change detector 2077. The statechange detector 2077 generates a reset signal in accordance with theinput information and supplies it to the WM analyzer 2076.

In the case in which the channel switching-based detection method (5) isemployed, a channel switching signal is input to the state changedetector 2077, and the state change detector 2077 generates a resetsignal in accordance with the input information and supplies it to theWM analyzer 2076. In this case, it is not necessarily needed to inputvideo data Di to the state change detector 2077 as in the constructionshown in FIG. 12, but the channel switching signal output from a userinterface or a similar device is input to the state change detector2077.

In the case in which the input signal-based detection method (6) isemployed, a change in the input signal is detected by means of aconstruction similar to that employed in the detection technique (1) onthe basis of a change in luminance of video data, and the state changedetector 2077 generates a reset signal in response to the detection of achange and supplies it to the WM analyzer 2076.

The state change detector 2077 monitors a change in one of the statesdescribed above or changes of a plurality of states to detect acontent-to-content transition. If a content-to-content transition isdetected, the state change detector 2077 outputs a reset signal to theWM analyzer 2076.

The copy control process performed when a reset signal is output fromthe state change detector 2077 is similar to that described above withreference to FIG. 8. In the example shown in FIG. 8, a digital watermarkfunctioning as copy control information indicating that copying shouldbe controlled in the Copy Once mode is embedded in a content providedduring a period A, and a digital watermark functioning as copy controlinformation indicating that copying is permitted in the Copy Free modeis embedded in a content provided during a period B.

Detection of a digital watermark from a content is performed repeatedlyfor each image frame. However, as described earlier, the levels ofdetected digital watermarks, that is, the detected levels, varydepending on the condition of the video data, and the digital watermarkscannot be accurately detected unless the detected levels are higher thana predetermined threshold (Th). Therefore, the digital watermarks areread only when the detected levels are higher than the threshold (Th).If a digital watermark includes copy control information, copying iscontrolled in accordance with the detected copy control information.More specifically, decision as to whether recording on a recordingmedium should be permitted or prohibited is made in accordance with thecontrol information, and the copy control information is rewritten fromCopy Once to No More Copy.

In FIG. 8, detection timing arrows (denoted by a, b, c, d, e, f, and g)indicate times at which digital watermarks having a level higher thanthe threshold (Th) is successfully detected. If a digital watermark isdetected, the process performed thereafter obeys the detectedinformation at least over a following period with a predetermined length(T). In the case of the content A, because the digital watermarkincluding the copy control information indicating that copying should becontrolled in the Copy Once mode is embedded in the content A, copyingis controlled in accordance with the copy control information indicatingthat copying should be controlled in the Copy Once mode. If no digitalwatermark is detected in a period with the predetermined length (T), thedetected information is determined to be “undefined”, that is, theprocess is performed assuming that that no control information isincluded in the content. In this case, the process may be performed in asimilar manner as in the Copy Free mode, as described earlier.Alternatively, CGMS information may be applied if the CGMS informationis sufficiently reliable.

In FIG. 8, at a time denoted by a detection timing arrow c, digitalwatermark information is detected from the content A, and the process isperformed in accordance with the detected copy control informationindicating Copy Once. Thereafter, at a time (denoted by an arrow d)within a following period of T, a digital watermark including copycontrol information indicating that copying should be controlled in theCopy Once mode is detected. After that, if the content is switched fromA to B, this content-to-content transition is detected by the statechange detector 2077, and a reset signal is output from the state changedetector 2077 to the WM analyzer 2076.

In response to the reset signal received from the state change detector2077, the WM analyzer 2076 resets the current copy control informationheld therein to the “undefined” state and outputs the copy controlinformation in the “undefined” state. Thus, as shown in FIG. 8, in aperiod immediately after that the content A is switched to the contentB, copy control is performed in the “undefined” mode until digitalwatermark information WM having a signal level higher than the thresholdis detected next. More specifically, during this period, the copycontrol may be performed in a similar manner as in the Copy Free mode,or performed in accordance with CGMS information if the CCMS informationis reliable.

Thereafter, if digital watermark information associated with the contentB is detected at a detection timing (an arrow e), that is, if digitalwatermark information having a signal level higher than the threshold(Th) is input from the despreader 2075 (FIG. 12) to the WM analyzer2076, an update request in accordance with copy control informationincluded in newly detected digital watermark information WM is output tothe WM information updater 4012 from the WM level evaluator 4011 of theWM analyzer shown in FIG. 13. In accordance with the update request, theWM information updater 4012 performs an updating process. In thisspecific case, because copy control information of Copy Free is added asdigital watermark information to the content B, the Copy Free mode isapplied in the process performed thereafter.

In the present embodiment, as described above, the state change detector2077 monitors a content-to-content transition and outputs a reset signalto the WM analyzer when a content-to-content transition is detected,thereby resetting the current control mode. This prevents the copycontrol information included in a previous content from beingincorrectly applied to a following content when a content-to-contenttransition occurs.

FIG. 14 shows processing flows in a process of updating/resettingdigital watermark information WM, performed by the WM analyzer 2076according to the present embodiment.

The WM level evaluator 4011 (FIG. 13) of the WM analyzer compares thesignal level of detected digital watermark information input from thedespreader 2075 (FIG. 12) with the predetermined threshold (Th) (stepS801). In this step, the signal level compared with the threshold (Th)may be an integral of detected digital watermark information, asdescribed earlier. If the signal level of the detected digital watermarkinformation is higher than the threshold (Th), the WM level evaluator4011 outputs, to the WM information updater 4012, an update request inaccordance with copy control information included in the detecteddigital watermark information WM. In accordance with the update request,the WM information updater 4012 updates the copy control informationrepresented in digital watermark information WM (step S803).

Because one or two pieces of copy control information are generated bythe despreader 2075 in the WM decoder 207 by means of despreading usingthe two PN code series PNa and PNb, the WM level evaluator 4011 selectsa piece of copy control information indicating a copy control modecloser to the never copy mode of the two pieces of copy controlinformation and outputs an update request, in accordance with theselected copy control information, to the WM information updater 4012(step S802).

On the other hand, if, in the comparison step (step S801) in which thesignal level of the detected digital watermark information is comparedwith the predetermined threshold (Th), the signal level is determined tobe lower than the threshold (Th), the holding timer measures the timeelapsed since latest digital watermark information WM was detected, anddetermines whether the elapsed time has reached a holding time T (stepS806).

After updating the copy control information in the digital watermarkinformation WM in step S803, if the elapsed time has not reached theholding time T, the process proceeds to step S804 to determine whether areset signal has been input. The reset signal detected in step S804 isthat which is generated by the state change detector 2077 for detectinga content-to-content transition and is input to the WM analyzer 2076.

If it is determined in step S804 that the reset signal is input to theWM analyzer 2076 from the state change detector 2077, the copy controlinformation represented in the digital watermark information WM that isheld in the WM analyzer 2076 and has been applied as control informationis reset to the “undefined” state. In a case in which it is determinedin step S806 that the time elapsed since the latest digital watermarkinformation WM was detected has reached the holding time T, the copycontrol information is also reset to the “undefined” state in step S805.

In the present invention, as described above, when a content-to-contenttransition occurs, a current content switched to from a previous contentcan be prevented from being erroneously subjected to copy controlaccording to copy control information assigned to the previous content.

In the specific example described above, two PN code series are detectedat the same time. Alternatively, two PN code series may be detectedseparately and time-sequentially. More specifically, detection using thecode series PNa is first performed. If the copy control mode designatedby the copy control information detected using the code series PNa isnot “Copy Once”, the designated copy control mode is employed as theresult of WM analysis. However, if the copy control mode is “Copy Once”,detection is further performed using the code series PNb, and the copycontrol mode is determined in accordance with the detected two pieces ofcopy control information. In this method, when analysis of digitalwatermark is performed again after resetting is performed, the analysisstarted with the detection using PNa. Alternatively, after detectionusing the code series PNa, detection using the code series PNb issubsequently performed regardless of whether the detected copy controlmode is “Copy Once” or not, and final decision is always made bycomparing the two detection results.

The process performed by the recording apparatus 200 after thecompletion of decryption is described below with reference to the flowchart shown in FIG. 15.

First, in step S101, the decoded digital watermark information WM outputfrom the WM decoder 207 is checked. In the next step S102, it isdetermined whether the digital watermark information WM designateseither “Never Copy” mode or the “No More Copy” mode. If either one ofmodes is designated, the process proceeds to step S103. In step S103,recording operation is disabled, and the recording process isterminated. In a case in which neither one of modes is designated, theprocess proceeds to step S104. The “Never Copy” mode is not detected forvideo information input via the digital input terminal. However, in thecase of video information input via the analog input terminal, the“Never Copy” mode can be detected.

In step S104, it is determined whether the digital watermark informationWM designates the “Copy Once” mode. If the “Copy Once” mode is notdesignated, then the possible mode is the “Copy Free” or the “undefined”mode, and thus the process jumps to step S106 in which the video data isscrambled. In the next step 107, the scrambled video data is recorded onthe RAM disk 30.

In the case in which the “Copy Once” mode is designated by the digitalwatermark information WM, the process proceeds to step S105. In stepS105, in accordance with the detected digital watermark information WM,the CGMS rewriter 209 rewrites the CGMS information into “11”, and theWM rewriter 208 rewrites the digital watermark information WM into “NoMore Copy”. Note that in this specific embodiment, as described earlier,the rewriting of the digital watermark information is actually performedby further superimposing digital watermark information WM designating“No More Copy” in addition to the existing digital watermarkinformation.

After completion of step S105, the process proceeds to step S106 toscramble the video data. In step S107, the scrambled video data isrecorded on the RAM disk 30. In this recording process, additionalinformation (scramble flag) indicating that the recorded information isscrambled is also recorded on the RAM disk 30.

In the case in which the digital watermark information WM designates the“Copy Free” mode or the “undefined” mode, the process may jump to stepS107 after step S104 so that the video data is recorded directly on theRAM disk 30 without performing scrambling. However, it is more desirableto perform scrambling (encryption) whenever recording on a RAM disk 30is performed, so that illegally copied information can be easilydetected when it is tried to be played back, as described later.

In the recording apparatus according to the present embodiment, asdescribed above, the CGMS information is rewritten in accordance withthe digital watermark information WM and recorded. As described earlier,it is very difficult to tamper with the digital watermark information WMto fraudulently copy video information, because the digital watermarkinformation is superimposed in the same ranges in the frequency domainand in the time domain as those of the video information. Therefore, itcan be expected that the CGMS information will be rewritten alwayscorrectly and recorded on the RAM disk 30.

This makes is possible for even an apparatus having a capability ofperforming generation-based copy control using only CGMS information tocorrectly perform copy control. Furthermore, effective copy control ispossible also in a case in which when information recorded on a RAM disk30 is played back and the played-back digital information is transmittedvia an IEEE1394 interface, transmission of video data and a decryptionkey is controlled in accordance with only CGMS information.

[Compliant Playback Apparatus]

An example of a construction of the compliant playback apparatus 300 isdescribed below with reference to FIGS. 16 to 19.

FIG. 16 is a block diagram showing the general construction of thecompliant playback apparatus 300. As shown in FIG. 16, informationrecorded on a disk 30 mounted on the playback apparatus 300 is read by areading unit 301 and supplied to a descrambler 302, a scramble detector303, and a disk type detector 304.

The scramble detector 303 extracts a scramble flag recorded asadditional information on the disk 30 and determines whether therecorded information is scrambled or not. Data indicating the detectionresult is supplied to a controller 310. Herein, it is assumed that whena ROM disk includes CGMS information having a value of “11” or digitalwatermark information designating the “Never Copy” copy control mode,that is, when the ROM disk is prohibited being copied, informationrecorded on the ROM disk is scrambled according to the CSS (ContentsScramble System) scheme.

The disk type detector 304 determines whether the mounted disk is a RAMdisk or a ROM disk, on the basis of, for example, TOC or directoryinformation. Data indicating the detected disk type is supplied to thecontroller 310.

The descrambler 302 descrambles the information scrambled by thescrambler 211 of the recording apparatus 200. In the case of informationrecorded on a RAM disk by a non-compliant recording apparatus, there isa possibility that the information is not scrambled. Such information isalso subjected to the descrambling process performed by the descrambler302. Therefore, if information recorded on a RAM disk by a non-compliantrecording apparatus is tried to be played back, the result is that thedescrambling causes the non-scrambled information to be converted into aseemingly scrambled form that cannot provide a normal picture or sound.

The descrambler 302 is also capable of descrambling CSS-scrambledinformation recorded on a ROM disk. The descrambling scheme employed bythe descrambler 302 is determined and controlled by the controller 310on the basis of data output from the disk type detector 304 andindicating whether the disk if a RAM disk or a ROM disk.

The data output from the descrambler 302 is supplied to a WM decoder 305and a playback permission/prohibition controller 306. The WM decoder 305extracts digital watermark information WM and decodes it. The decodeddigital watermark information WM is supplied to the controller 310.

The controller 310 determines whether to permit or prohibit playback, onthe basis of the detection result supplied from the scramble detector303, the detection result supplied from the disk type detector 304, andthe decoded digital watermark information WM. In a case in which thecontroller 310 determines that playback is prohibited, the controller310 supplies control signal to the playback permission/prohibitioncontroller 306 to disable the process performed by parts following theplayback permission/prohibition controller 306. Thus, when it isdetermined that playback is prohibited, neither an analog playbacksignal nor a digital signal via the IEEE1394 interface is output.

In the case in which it is determined that playback is permitted, theprocess performed by parts following the playback permission/prohibitioncontroller 306 is enabled, and video data output from the playbackpermission/prohibition controller 306 is supplied to a CGMS rewriter307. The CGMS rewriter 307 rewrites the CGMS information, as with theset-top box 100, so that the CGMS information becomes consistent withthe digital watermark information WM extracted and decoded by the WMdecoder 305. More specifically, if the signal level of detected digitalwatermark information is higher than the threshold Th and the elapsedtime is within the holding time T, the CGMS information is rewritten inaccordance with the digital watermark information WM.

However, in a case in which digital watermark information having asignal level higher than the threshold Th is not detected within aperiod of holding time T and digital watermark information is determinedto be “undefined”, or in a case in which the a content-to-contenttransition is detected by the state change detector disposed in the WMdecoder 305 and a reset signal is input to the WM analyzer whereby thedigital watermark information is determined to be “undefined”, rewritingof the CGMS information according to the digital watermark informationWM is not performed.

Compressed digital video data output from the CGMS rewriter 307 issupplied to a video data decoder 308 to decode the MPEG-compressed datainto a decompressed form. The resultant data decoded into thedecompressed form is supplied to a D/A converter 309 to convert it intoan analog signal. The resultant analog signal is supplied to an externalelectronic device via the analog output terminal 300 a.

The WM decoder 305 is constructed in the same manner as the WM decoder207 shown in FIG. 10. That is, in the WM decoder 305, if a state changedetector detects a content-to-content transition, the state changedetector outputs a reset signal to a WM analyzer. Tf the WM analyzerreceives the reset signal from the state change detector, the WManalyzer outputs an “undefined”-state signal.

The compressed digital video data from the CGMS rewriter 307 isdigitally output via an IEEE1394 interface bus. In this outputtingprocess, as described earlier, the IEEE1394 secure bus prevents the datafrom being fraudulently copied.

More specifically, the data output from the CGMS rewriter 307 issupplied to an encryptor 311, and the encryptor 311 encrypts thereceived video data in the compressed form, under the control of thecontroller 310, by using an encryption key that is changed fromcommunication to communication. The encryption performed by theencryptor 311 is performed in a similar manner as is performed by theencryptor 108 of the set-top box 100 described above.

The encrypted data output from the encryptor 311 is supplied to adestination electronic device via an IEEE1394 interface 312 and furthervia an output terminal 300 b. In this process, the IEEE1394 interface312 output the data after converting it into a form which satisfies theIEEE1394 interface specifications.

Furthermore, in this process, the controller 310 communicates with thedestination device via the IEEE1394 interface 312 to determine whetherthe destination device is a compliant device. If the destination deviceis a compliant device, the controller 110 further determines whether thedestination device is a recording apparatus.

Thereafter, the controller 310 determines whether decryption keyinformation necessary to decrypt the encryption performed by theencryptor 311 should be transmitted to the destination device, on thebasis of, in this specific embodiment, the copy control informationdecoded by the WM decoder 305 and the type of the destination deviceindicated by information given through the IEEE1394 interface 312. In acase in which plural pieces of copy control information are output fromthe WM decoder 305, the controller 310 employs copy control informationhaving a control mode closest to the Never Copy mode.

In a case in which the destination device is a non-compliant apparatus,the decryption key information is not transmitted to the destinationdevice Even when the destination device is a compliant apparatus, if thedestination device is a recording apparatus and if the “No More Copy” or“Never Copy” mode is designated by the digital watermark information WM,the decryption key information is not transmitted to the destinationdevice.

The processing operation performed by the compliant playback apparatus300 according to the present embodiment is described below withreference to FIGS. 17 to 19.

In the playback apparatus 300, in the first step S201, it is determinedwhether data recorded on a disk mounted on the playback apparatus 300 isscrambled. The scrambling to be detected in this step may have beenperformed by the scrambler 211 of the recording apparatus 200 or mayhave been by means of the CSS scheme on a ROM disk. If the data isscrambled, the process proceeds to step S202 to further determinewhether the disk is a ROM disk or a RAM disk.

If the disk is a RAM disk, the process proceeds to step S203 to checkthe digital watermark information WM. In the next step S204, it isdetermined whether the copy control mode designated by the digitalwatermark information WM is “Copy Once” or the “Never Copy”. If eitherone of these modes is designated, the process proceeds to step S205 todisable the playing-back operation.

The reason why playback is disabled in the case in which it isdetermined in step S204 that the digital watermark information WMdesignates the “Copy Once” mode is that the fact that the data isscrambled indicates that the disk 30 is a RAM disk and that the data hasbeen recorded on that RAM disk using the compliant recording apparatus200, but, nevertheless, the fact that the digital watermark informationWM designates the “Copy Once” mode indicates that the data has beenillegally copied.

The reason for the above conclusion is that if data is recorded on a RAMdisk using the compliant recording apparatus 200, digital watermarkinformation WM must be rewritten from “Copy Once” to “No More Copy”.

The reason why when the disk is a RAM disk, playback is disabled if thedigital watermark information WM indicates the “Never Copy” mode is thatthe data recorded on this RAM disk must be that illegally copied from aROM having digital watermark information WM designating the “Never Copy”mode.

In a case in which it is determined in step S204 that the copy controlmode designated by the digital watermark information WM is neither “CopyOnce” nor the “Never Copy”, the process proceeds to step S206 to enablethe playing-back operation. In the next step S210, the CGMS information(CGMS-D information) associated with the digital video data is rewrittenin accordance with the digital watermark information WM detected by theWM decoder 305 so that the digital watermark information WM and the CGMSinformation become consistent with each other.

More specifically, if the signal level of detected digital watermarkinformation is higher than the threshold Th and the elapsed time iswithin the holding time T, the CGMS information is rewritten inaccordance with the digital watermark information WM. However, in a casein which digital watermark information having a signal level higher thanthe threshold Th is not detected within a period of holding time T anddigital watermark information is determined to be “undefined”, or in acase in which the a content-to-content transition is detected by thestate change detector of the WM decoder 305 and a reset signal is inputto the WM analyzer whereby the digital watermark information isdetermined to be “undefined”, rewriting of the CGMS informationaccording to the digital watermark information WM is not performed.

Thereafter, in step 211, digital data is output via the IEEE1394interface.

In the case in which it is determined in step S202 that the mounted diskis a ROM disk, the process proceeds to step S207 to check the digitalwatermark information WM. In the next step S208, it is determinedwhether the digital watermark information WM designates the “Never Copy”mode. This determination is performed in order to confirm that the datahas been CSS-scrambled and the digital watermark information correctlydesignates the “Never Copy” mode that should be designated in any ROMdisk that is prohibited from being copied.

If it is determined in this step S208 that the digital watermarkinformation neither designates the “Never Copy” mode nor is in the“Undefined” state, it is determined that the ROM disk has been tamperedwith. In this case, the process proceeds to step S209 to disableplayback. If the “Never Copy” mode is correctly designated or thedigital watermark information WM is in the “undefined” state, theprocess proceeds to step S206 to enable the playing-back operation. Inthis case, the process then proceeds to step S210 to rewrite the CGMSinformation into “11”. (Note that rewriting is not performed when thedigital watermark information is in the “Undefined” state.) Thereafter,the process further proceeds to step S212 to output digital data.

In a case in which it is determined in step S201 that the informationrecorded on the disk is not scrambled, the process proceeds to step S212shown in FIG. 18 to further determine whether the disk is a ROM disk ora RAM disk. If the disk is determined to be a RAM disk, the processproceeds to step S213 to check the digital watermark information WM.

In the next step S214, it is determined whether the digital watermarkinformation WM either designates the “Copy Free” mode or is in the“Undefined” state. If no, it is determined that illegal tampering hasbeen performed, and the process proceeds to step S215 to disableplayback. On the other hand, if it is determined in step S214 that thedigital watermark information WM either designates the “Copy Free” modeor is in the “Undefined” state, the process proceeds to step S216 toenable playback.

In the case in which it is determined in step S212 that the disk is aROM disk, the process proceeds to step S217 to check the digitalwatermark information WM. Then it is determined whether the digitalwatermark information WM designates either one of modes including “CopyFree”, “No More Copy”, “One Copy”, and “Undefined”. If yes, then theprocess proceeds to step S216 to enable playback. However, if no, theprocess proceeds to step S219 to disable playback.

That is, in the present embodiment, when the disk is a ROM disk, if thedigital watermark WM designates the “Never Copy” mode, the data recordedon the ROM disk must have been CSS-scrambled. In other words, if thedata has not been scrambled and if the “Never Copy” mode is designated,then it cab be concluded that the data has been subjected to illegaltampering, and thus playback is disabled.

Now, the outputting process in step S211 is described in more detailbelow. FIG. 19 is a flow chart showing the outputting digital data viathe IEEE1394 interface. This process is performed by means of IEEE1394secure bus described earlier.

In step S301, it is determined whether playback is permitted. Ifplayback is prohibited, the outputting routine is terminated. However,if playback is permitted, the process proceeds to step S302. In stepS302, communication with an destination device is performed via theIEEE1394 bus to determine whether the destination device is a compliantapparatus. If the destination device is not a compliant apparatus, theprocess proceeds to step S308 in which encrypted (MPEG-compressed)digital information is output. In this case, a decryption key necessaryto decrypt the encrypted digital data is not transmitted to thedestination device. This makes it impossible for any non-compliantapparatus to decrypt encrypted data.

In a case in which it is determined in step S302 that the destinationdevice is a compliant apparatus, the process proceeds to step S303 tofurther determine whether the compliant destination device is arecording apparatus. If the destination device is not a recordingapparatus, the process jumps to step S306, in which digital information(MPEG-compressed data) is encrypted and output together with adecryption key necessary to decrypt the encrypted digital information tothe destination device.

In a case in which it is determined in step S303 that the destinationdevice is a compliant recording apparatus, the process proceeds to stepS304 to further determine whether the disk is a ROM disk or a RAM disk.If the disk is a RAM disk, the process proceeds to step S305, in which,in the present embodiment, it is further determined whether the digitalwatermark information WM designates either the “No More Copy” mode orthe “One Copy” mode.

If the digital watermark information designates neither the “No MoreCopy” mode nor the “One Copy” mode, the process proceeds to step S306,in which digital information (MPEG-compressed data) is encrypted andoutput together with a decryption key necessary to decrypt the encrypteddigital information to the destination device. If the digital watermarkinformation designates either “No More Copy” mode or the “One Copy”mode, the process proceeds to step S308, in which digital information(MPEG-compressed data) is encrypted and output to the destinationdevice, but a decryption key necessary to decrypt the encrypted digitalinformation is not transmitted to the destination device.

If it is determined in step S304 that the disk is a ROM disk, theprocess proceeds to step S307 to determine whether the digital watermarkinformation either designates the “Copy Free” mode or is in the“Undefined” state. If yes, the process proceeds to step S306, in whichdigital information (MPEG-compressed data) is encrypted and outputtogether with a decryption key necessary to decrypt the encrypteddigital information to the destination device. However, if no, theprocess proceeds to step S308, and digital information (MPEG-compresseddata) is encrypted and output to the destination device, but adecryption key necessary to decrypt the encrypted digital information isnot transmitted to the destination device.

In the playback apparatus according to the present embodiment, asdescribed above, when digital video data is output, the copyright of thedigital video data is protected by means of the secure bus of theIEEE1394 interface, and CGMS information included in the video data tobe output is rewritten in accordance with digital watermark informationWM having very high resistance against illegal tampering so that theCGMS information becomes consistent with the digital watermarkinformation WM.

This ensures that when the digital video data received from the playbackapparatus is recorded by a recording apparatus, copy control iscorrectly performed in accordance with the CGMS information.

In the playback apparatus 300, the IEEE1394 interface may determinewhether to transmit the decryption key to the destination device, on thebasis of CGMS information rewritten by the CGMS rewriter 307. In thiscase, when the destination device is a compliant recording apparatus, ifthe CGMS information has a value of “11”, the decryption key informationis not transmitted to the destination device.

Also in this playback apparatus 300, as with the set-top box 100described earlier, when an analog video signal is output from the D/Aconverter 309, CGMS-A information described in accordance with thedigital watermark information WM may be added to the analog videosignal.

A decoder for decoding CGMS information added to played-back video datamay be provided, and, if comparison between the digital watermarkinformation WM decoded by the WM decoder 305 and the CGMS informationdecoded by the CGMS decoder indicates that the copy control modedesignated by the CGMS information is closer to the Never Copy mode, theCGMS information may not be rewritten. Of course, if there is noinconsistency between the CGMS information and the digital watermarkinformation WM, the CGMS information may not be rewritten.

[Modifications]

In the above-described embodiment of the playback apparatus, playbackrestriction is accomplished by disabling any playback operation.Alternatively, restriction may be achieved by disabling an informationsignal from being reproduced into a normal form. For example, when theinformation signal is a video signal, the video signal may be convertedinto a form that cannot be visually understood. In the case of an audiosignal, noise may be generated. That is, any restriction method may beemployed as long as it can substantially prevent a normal informationsignal from being played back. When playback of a disk is prohibited, amessage indicating, for example, that the disk is cannot be played backbecause the disk includes illegally copied data may be visuallydisplayed on a screen or acoustically output from a speaker.

In the embodiments described above, CGMS information is employed asadditional information that is added together with digital watermarkinformation. As a matter of course, the additional information is notlimited to CGMS information.

The digital watermark information is not limited to spectrum-spreaddigital watermark information employed in the embodiments describedabove. The digital watermark information may be represented in manyother forms. For example, additional information with a low signal levelmay be superimposed on a digital signal. When data is compressed bymeans of MPEG compression or the like using an orthogonaltransformation, additional information with a low signal level may besuperimposed on frequency components of the compressed data such thatthe additional information seems like noise. Another technique ofsuperimposing additional information is to divide a screen into aplurality of small areas with predetermined sizes and paste a unitdigital watermark pattern to each small area thereby superimposing thedigital watermark on video signal.

The rewritable recording medium is not limited to recording disks, butother types of recording media such as a semiconductor memory or amagnetic tape may also be employed. The information signal is notlimited to video signals, but the information signal may be an audiosignal.

Although in the embodiments described above, the recording apparatus andthe playback apparatus are constructed in separated forms, the presentinvention may also be applied to an apparatus in which the recordingapparatus and the playback apparatus are integrated. Although in theabove-described embodiments according to the present invention, theset-top box is employed as the apparatus for outputting an informationsignal, the present invention may also be applied to a broadcastingapparatus or a computer that is connected to a network to re-transmitdigital video data acquired from another computer or a server over thenetwork.

Although in the embodiments described above, not only CGMS informationbut also digital watermark information is rewritten, only CGMSinformation may be rewritten without rewriting digital watermarkinformation.

The present invention has been described in detail above with referenceto particular embodiments. It will be apparent to those skilled in theart that various modifications and substitution to those embodiments maybe made in the embodiment chosen for illustration without departing fromthe spirit and scope of the invention. That is, the embodiments havebeen described above by way of example and not limitation. The scope ofthe invention is to be determined solely by the claims.

Note that processes disclosed herein in the present description may beexecuted by hardware, software, or a combination of hardware andsoftware. Execution of processes by software may be accomplished byinstalling a program, in which a sequence of processing steps isdescribed, into a memory disposed in a computer embedded in dedicatedhardware, or by installing such a program into a general-purposecomputer capable of executing various kinds of processes.

The program may be stored, in advance, on a hard disk serving as astorage medium or in a ROM (Read Only Memory). Alternatively, theprogram may be stored (recorded) temporarily or permanently on aremovable storage medium such as a floppy disk, a CD-ROM (Compact DiscRead Only Memory), an MO (Magnetooptical) disk, a DVD (Digital VersatileDisc), a magnetic disk, or a semiconductor memory. Such a removablerecording medium may be provided in the form of so-called packagesoftware.

Instead of installing the program from such a removable storage mediumonto the computer, the program may also be transferred to the computerfrom a download site by means of radio transmission or by means of cabletransmission via a network such as an LAN (Local Area Network) or theInternet. In this case, if the computer receives the program transmittedin such a manner, the computer installs the program on a storage mediumsuch as a hard disk disposed in the computer.

The processes disclosed in the present description may be executedtime-sequentially in the same order as processing steps are described inthe program, or may be executed in parallel or individually depending onthe capacity or capability of an apparatus which executes processes. Inthe present description, the term “system” is used to describe a logicalcollection of a plurality of devices, and it is not necessarily requiredthat the plurality of devices are disposed in a single case.

INDUSTRIAL APPLICABILITY

In the data processing apparatus, the data processing method, and theprogram, according to the present invention, as described above, copycontrol information in the form of digital watermark information (WM) isembedded in a content to control copying of the content in accordancewith the embedded copy control information, such that acontent-to-content transition is detected by detecting a change in acontent state such as a change in image luminance, or a change in copycontrol information associated with a content or is detected on thebasis of a flag, a descriptor, or channel switching; and in response todetection of a content-to-content transition, a reset signal is outputto the WM analyzer that is outputting the copy control information toreset the current copy control information into a “undefined” state sothat copy control is performed in a mode such as a “Copy Free” controlmode assigned to the “undefined” state, thereby ensuring that when aprevious content is switched to a present content, the present contentis prevented from being incorrectly subjected to a copy control processaccording to copy control information assigned to the previous content.

Furthermore, in the data processing apparatus, the data processingmethod, and the program, according to the present invention, asdescribed above, copy control information in the form of digitalwatermark information (WM) is embedded in a content to control copyingof the content in accordance with the embedded copy control information,such that when the digital watermark information (WM) is in an undefinedstate, the reliability of information such as CGMS information otherthan digital watermark information (WM) is evaluated by checkingconsistency between the information other than the digital watermarkinformation and the digital watermark information (WM) on the basis ofhistory information, and, if the information such as CGMS informationother than the digital watermark information (WM) is determined highlyreliable, copy control is performed in accordance with the informationother than the digital watermark information (WM), thereby ensuring thatcopy control is performed in a highly reliable fashion.

1. A digital watermark decoding system for use in data processingapparatus for performing at least one of a data recording process, adata playing-back process, and a data inputting/outputting process, inwhich copy control information represented in digital watermarkinformation is detected, and copying of data is controlled in accordancewith the detected copy control information included in the digitalwatermark information, said digital watermark decoding system detectinga digital watermark embedded in a content and outputting detected copycontrol information as control information applied to a content to beprocessed, said digital watermark decoding system comprising: statechange detection means for detecting a transition from a content toanother content having a possibility that copy control informationembedded therein is different from copy control information embedded inthe former content, and outputting a reset signal to digital watermarkinformation analysis means in response to detecting of a state changecorresponding to the content transition; and digital watermarkinformation analysis means for resetting control information applied tothe content in accordance with the reset signal received from the statechange detection means, and outputting, as control information to beapplied to the content, undefined control information corresponding tonon-detection of a digital watermark, wherein when the digital watermarkinformation output from the digital watermark information analysis meansis undefined, and when a content to be processed includes copy controlinformation, added thereto, other than digital watermark information,the copy control information other than the digital watermarkinformation is employed as control information to be applied to thecontent.
 2. The digital watermark decoding system according to claim 1,wherein when the digital watermark information output from the digitalwatermark information analysis means is undefined, and when a content tobe processed includes copy control information, added thereto, otherthan digital watermark information, history of the copy controlinformation other than digital watermark information and history of copycontrol information described in the digital watermark information arechecked to determine whether these two kinds of copy control informationwere consistent with each other over a predetermined period, and, onlywhen it is determined that the two kinds of copy control informationwere consistent with each other over that period, the copy controlinformation other than digital watermark information is employed as copycontrol information to be applied to the content.
 3. The digitalwatermark decoding system according to claim 1, wherein said copycontrol information other than digital watermark information is copygeneration management system information.
 4. The digital watermarkdecoding system according to claim 1, wherein the state change detectionmeans monitors a change in signal information of a content beingprocessed; and, when a change greater than a predetermined threshold isdetected, the state change detection means determines that acontent-to-content transition has occurred, and the state changedetection means outputs a reset signal to the digital watermarkinformation analysis means.
 5. The digital watermark decoding systemaccording to claim 1, wherein the state change detection means monitorsa change in copy control information serving as additional informationother than digital watermark information, added to a content beingprocessed; and, when a change is detected, the state change detectionmeans determines that a content-to-content transition has occurred, andthe state change detection means outputs a reset signal to the digitalwatermark information analysis means.
 6. The digital watermark decodingsystem according to claim 1, wherein the state change detection meansmonitors a change in one of a descriptor and a flag serving asadditional information other than digital watermark information, addedto a content being processed; and, when a change is detected, the statechange detection means determines that a content-to-content transitionhas occurred, and the state change detection means outputs a resetsignal to the digital watermark information analysis means.
 7. Thedigital watermark decoding system according to claim 1, wherein thestate change detection means monitors channel switching; and, whenchannel switching is detected, the state change detection meansdetermines that a content-to-content transition has occurred, and thestate change detection means outputs a reset signal to the digitalwatermark information analysis means.
 8. The digital watermark decodingsystem according to claim 1, wherein the state change detection meansmonitors presence/absence of an input signal and determines that acontent-to-content transition has occurred when one of apresence-to-absence transition, an absence-to-presence transition, and apresence-to-absence-to-presence transition is detected, and the statechange detection means outputs a reset signal to the digital watermarkinformation analysis means in response to the detection of thecontent-to-content transition.
 9. A digital watermark decoding methodfor use with a data processing method of performing at least one of adata recording process, a data playing-back process, and a datainputting/outputting process, in which copy control informationrepresented in digital watermark information is detected, and copying ofdata is controlled in accordance with the detected copy controlinformation included in the digital watermark information, said digitalwatermark decoding method including detecting a digital watermarkembedded in a content and outputting detected copy control informationas control information applied to a content to be processed, saiddigital watermark decoding method comprising the steps of: detecting atransition from a content to another content having a possibility thatcopy control information embedded therein is different from copy controlinformation embedded in the former content, and outputting a resetsignal to digital watermark information analysis means in response todetecting of a state change corresponding to the content transition; andresetting control information applied to the content in accordance withthe input reset signal, and outputting, as control information to beapplied to the content, undefined control information corresponding tonon-detection of a digital watermark, wherein when the digital watermarkinformation output from the digital watermark information analysis meansis undefined, and when a content to be processed includes copy controlinformation, added thereto, other than digital watermark information,the copy control information other than the digital watermarkinformation is employed as control information to be applied to thecontent.
 10. The digital watermark decoding method according to claim 9,wherein when the digital watermark information output from the digitalwatermark information analysis means is undefined, and when a content tobe processed includes copy control information, added thereto, otherthan digital watermark information, a history of the copy controlinformation other than digital watermark information and history of copycontrol information described in the digital watermark information arechecked to determine whether these two kinds of copy control informationwere consistent with each other over a predetermined period, and onlywhen it is determined that the two kinds of copy control informationwere consistent with each other over that period, the copy controlinformation other than digital watermark information is employed as copycontrol information to be applied to the content.
 11. The digitalwatermark decoding method according to claim 9, wherein said copycontrol information other than digital watermark information is copygeneration management system information.
 12. The digital watermarkdecoding method according to claim 9, wherein the state change detectingstep includes monitoring a change in signal information of a contentbeing processed; and, when a change greater than a predeterminedthreshold is detected, determining that a content-to-content transitionhas occurred and outputting a reset signal to the digital watermarkinformation analysis means.
 13. The digital watermark decoding methodaccording to claim 9, wherein the state change detecting step includesmonitoring a change in copy control information serving as additionalinformation other than digital watermark information, added to a contentbeing processed; and, when a change is detected, determining that acontent-to-content transition has occurred and outputting a reset signalto the digital watermark information analysis means.
 14. The digitalwatermark decoding method according to claim 9, wherein the state changedetecting step includes monitoring one of a change in a descriptor and aflag serving as additional information other than digital watermarkinformation, added to a content being processed; and when a change isdetected, determining that a content-to-content transition has occurredand outputting a reset signal to the digital watermark informationanalysis means.
 15. The digital watermark decoding method according toclaim 9, wherein the state change detecting step includes monitoringchannel switching; and, when channel switching is detected, determiningthat a content-to-content transition has occurred, and outputting areset signal to the digital watermark information analysis means. 16.The digital watermark decoding method according to claim 9, wherein thestate change detecting step includes monitoring a presence/absence of aninput signal, determining that a content-to-content transition hasoccurred when one of a presence-to-absence transition, anabsence-to-presence transition, and a presence-to-absence-to-presencetransition is detected, and outputting a reset signal to the digitalwatermark information analysis means in response to detection of thecontent-to-content transition.
 17. A digital watermark decoding methodfor use in a computer program for causing a computer system to executeat least one of a data recording process, a data playing-back process,and a data inputting/outputting process, in which copy controlinformation represented in digital watermark information is detected,and copying of data is controlled in accordance with the detected copycontrol information included in the digital watermark information, saiddigital watermark decoding method including detecting a digitalwatermark embedded in a content and outputting detected copy controlinformation as control information applied to a content to be processed,said digital watermark decoding method comprising the steps of:detecting a transition from a content to another content having apossibility that copy control information embedded therein is differentfrom copy control information embedded in the former content, andoutputting a reset signal to digital watermark information analysismeans in response to detecting of a state change corresponding to thecontent transition; and resetting control information applied to thecontent in accordance with the input reset signal, and outputting, ascontrol information to be applied to the content, undefined controlinformation corresponding to non-detection of a digital watermark,wherein when the digital watermark information output from the digitalwatermark information analysis means is undefined, and when a content tobe processed includes copy control information, added thereto, otherthan digital watermark information, the copy control information otherthan the digital watermark information is employed as controlinformation to be applied to the content.